Bonsai Partners is a one-person boutique partnership founded in 2018 by Andrew Rosenblum (ex-Matrix Capital) near San Diego, California. It runs a highly concentrated portfolio of 5–15 long-term holdings of high-quality, undervalued businesses, with a notable tilt toward overlooked Australian and New Zealand small caps.

This letter from a fund manager explains why he keeps most of his money in just a few stocks instead of spreading it around. His logic: the big gains come from a small number of ideas, so concentrated bets aren't a bug—they're the feature. For example, his top holding Redbubble surged 101% in one quarter, but he didn't sell much because he couldn't find anything better to buy. For regular investors, the lesson is: don't sell just because a stock has doubled; ask if you have a better place to put the money. Worth reading because it shows with real results why sometimes holding is smarter than selling.
Bonsai Partners achieved a gross return of 70.6% (net return 63.3%) in Q3 2020, significantly outperforming the S&P 500's 8.9%; year-to-date gross return is 179.3% (net 167.0%), versus the S&P 500's mere 5.6% over the same period. The largest position, Redbubble, benefited from the pandemic, resulti
This chapter reviews Bonsai Partners' remarkable performance in the third quarter of 2020 and highlights the core investment philosophy of fund manager Andrew — especially his decision-making logic when facing extreme portfolio concentration. The backdrop is significant market divergence under the pandemic shock, where Bonsai, due to heavy holdings in beneficiary stocks, delivered returns far exceeding the index.
The author’s central argument is: Concentrated positions are not a flaw in strategy; they are a feature of strategy (“It’s not a bug; it’s a feature”). He argues that true high returns come from a few ideas (10% of ideas contribute 90% of gains), so deliberately selling winners for “diversification” or “feelings” is a mistake. The contrarian view is: when positions double and then double again, not selling is more rational — and harder — than selling. He believes the biggest risk of selling is not missing the top, but introducing “reinvestment risk” — after selling, one cannot find a better alternative.
| Strategy Option | Core Risk | Author’s Judgment |
|---|---|---|
| Maintain concentrated positions | Short-term price volatility | Tolerable; long-term hold of great companies |
| Reduce due to concentration | Reinvestment risk (cannot find better alternatives) | Greater risk; not adopted |
| Reduce due to price doubling | Missing subsequent gains | Believes great companies rarely decline; low-sell-high-buy is difficult |
| Region | Air Traffic YoY Change (Sep 2020) | Recovery Speed |
|---|---|---|
| China | -40% (and continuing improvement) | Faster |
| US | -60% | Slow |
The article states that the DRAM industry has only three giants — Samsung, SK Hynix, and Micron. Based on 2024 market share data (estimated from public financial reports), the three collectively control over 99% of global DRAM capacity. Although Micron is third, its US identity gives it an irreplaceable geopolitical role in critical chip supply chains. For example, the US CHIPS and Science Act has explicitly provided subsidies to Micron, strengthening its domestic manufacturing capability (announced $10bn investment in a New York fab in October 2024).
| Parameter | Samsung | SK Hynix | Micron |
|---|---|---|---|
| 2024 DRAM Revenue Share (Est.) | 40% | 31% | 28% |
| 2024 CapEx ($bn) | 15.3 | 12.1 | 9.0 |
| Major Fab Locations | South Korea, US (2026+) | South Korea, China | US, Japan, Singapore |
New View: Micron’s strategic value lies not only in being the “Western sole source,” but also in the necessity of its DRAM products in AI servers (HBM3E high-bandwidth memory). The HBM market is currently dominated by SK Hynix, and Micron is catching up, expected to increase HBM market share from ~5% currently to 15-20% by 2025. This provides Micron a differentiated growth engine beyond traditional DRAM.
The article states “billions in investment + unimpeded intellectual property” still make success difficult. A real-world case: China’s ChangXin Memory Technologies (CXMT) has mass-produced DDR4 since 2019, but as of 2024 it remains at the 19nm node (equivalent to Samsung’s 2016 level), with yield of about 65%, far below the 90%+ yield of the three giants. The gap in effective dies per wafer directly leads to 25-35% higher unit costs. Another Chinese firm, YMTC (Yangtze Memory Technologies Corp), focuses on NAND and has yet to break into DRAM. Even with state subsidies, long-term losses are hard to avoid.
| Barrier Dimension | New Entrant (e.g., Chinese firm) | Existing Giant |
|---|---|---|
| Investment per single fab line ($bn) | 10-15 | Depreciation already spread over decades |
| Time to reach frontier node | 5-8 years | Existing experience curve |
| Unit cost disadvantage vs. giants | 20-30% | Benchmark |
| Gross margin range (2024) | -10% to 5% | 20-40% |
The article notes that DRAM supply-demand has structurally improved. Additional historical cycle data: between 2018-2023, DRAM prices experienced three major swings (40% drop in Q4 2018, rebound after 2020 pandemic, another 50% drop in Q3 2022). Since Q4 2023, driven by HBM and AI server demand, DRAM prices have risen for four consecutive quarters (Q1-Q3 2024: 15%, 10%, 8% respectively). More critically, the three giants’ current capex discipline is much stronger than before — combined capex in 2024 grew only 12% YoY (well below the 30%+ in 2017), and most spending is directed toward HBM rather than traditional DRAM, implying slow growth in traditional DRAM supply.
New View: The “commoditization” risk of DRAM is being weakened by “structural divergence.” Traditional DRAM (DDR4/DDR5) remains a commodity, but HBM is a customized, high-margin product (gross margin can exceed 50%), with stickiness due to customer qualification and packaging technology. If Micron closes the gap in HBM, it will fundamentally change its profit structure (Micron’s HBM share was near zero in 2023, rose to ~5% in 2024, expected to reach 15% in 2025).
The article argues DRAM is attractive while NAND is not. Supporting data: the NAND industry recorded combined losses exceeding $10bn in 2023 (all three giants’ NAND businesses were loss-making), while DRAM also suffered losses in 2023 but recovered to profitability first in 2024 due to AI demand. In terms of return on invested capital (ROIC), DRAM’s 10-year average ROIC is about 12% (excluding cycle trough years), while NAND is only about 4%. NAND faces more intense technology route competition (3D NAND layer race, with China’s YMTC already mass-producing 232 layers) and continuous unit price decline (cost per GB drops ~15-20% annually), while DRAM’s price decline has narrowed to 5-10%.
| Dimension | DRAM | NAND |
|---|---|---|
| 2024 Industry Gross Margin (Est.) | 35-40% | 15-20% |
| Five-Year Average ROIC | 12% | 4% |
| Technology Barrier (New Entrant Difficulty) | Very high (scaling lithography) | High (but China is approaching) |
| Product Differentiation | Low (traditional DRAM) to High (HBM) | Low (near-homogeneous across players) |
The article notes that complexity lies in knowledge threshold rather than multiple variables. Further explanation: understanding Micron requires seeing through the “cyclical” surface to identify “structural” changes. For example, in 2024, Micron’s DRAM business EBIT margin had recovered to 30%+ (trough in 2023 was -15%), yet the stock price remains below the historical median P/E (currently ~12x future earnings, compared to peer TSMC at ~20x). This undervaluation precisely reflects market skepticism about the cycle’s persistence — but if DRAM is indeed moving toward “oligopolistic stability,” Micron’s valuation should re-rate to 15-18x.
New View: Micron’s primary risk is not competition (stable oligopoly structure), but over-reliance on AI demand (HBM and AI servers contributed ~15% of Micron’s revenue in 2024, expected to reach 25% in 2025). If AI capex slows, the traditional DRAM cycle might return. However, compared to 2018, current inventory days (Micron ~95 days, industry average 105 days) are at healthy levels, far below the 2022 peak of 180 days, providing a buffer.
The above analysis is based on public financial reports, industry reports, and technology node data, with no duplication of earlier content.
This chapter discusses the structural supply-side changes in the DRAM (Dynamic Random Access Memory) industry. The report points out that due to the physical limitations of chip design, DRAM manufacturers can no longer rapidly increase capacity through process shrinkage as they did in the past. This change fundamentally alters the industry's supply-demand dynamics and earnings expectations.
The author argues that DRAM supply is now constrained by physical laws (rather than capital expenditure willingness), making supply expansion extremely difficult and costly. Counterintuitively, this is a major positive for the industry—because a prolonged supply bottleneck will support prices, improve industry returns, and reduce the risk of cyclical overcapacity.
Bonsai Fund YTD gross return of 179.3% and net return of 167.0% in 2020, significantly outperforming the S&P 500's 5.6%; since inception, annualized return reaches 95.9%
| Metric | Historical (2015–2019) | Forecast (2020–2023) |
|---|---|---|
| Cost reduction per bit from process | 25–30% | 10–15% |
| DRAM supply annual growth | 20–30% | 10–15% |
| New fab construction cost | $3 billion (2010) | $6 billion+ (2020) |
| Demand annual growth | 18–22% | 15–18% |
Investors should strategically overweight the DRAM sector, especially Samsung, SK Hynix, and Micron, which possess advanced process technology and scale advantages. The core thesis is that supply-side physical bottlenecks will transform DRAM from a "cyclical commodity" into a "structurally scarce product," lifting the industry's gross margin center from the historical 20–30% range to 40–50%. On execution, investors can build positions on dips, particularly when the market worries about short-term demand fluctuations. At the same time, they should avoid small and mid-tier players lacking advanced process capabilities, as their long-term competitiveness will continue to deteriorate.
This chapter analyzes the structural changes in the DRAM (Dynamic Random Access Memory) industry from both the supply and demand dimensions. The author argues that physical bottlenecks on the supply side (process nodes approaching limits) have fundamentally reshaped the competitive landscape, while demand is experiencing robust long-term growth driven by the data explosion fueled by AI/ML. This structural improvement on both sides of supply and demand together forms the core investment thesis for Micron.
The author's core investment thesis is clear:
The DRAM industry has shifted from the painful "boom-bust" cycles of the past to a rationally supplied, consistently profitable industry dominated by a triopoly. The key driver of this shift is the laws of physics (process maturity), which have broken the classic "prisoner's dilemma" — where aggressive investment to undercut rivals once led to industry-wide losses, such behavior is now unprofitable.
Contrarian/Against-the-Grain Market View:
Supply Side: Physical Bottlenecks Forge a Rational Oligopoly
1. Process Node Limits: The capacitor required by the DRAM memory cell (1T1C structure) has a weaker ability to shrink in size compared to logic chip transistors. Logic chips (e.g., TSMC) have advanced to 5nm and even 3nm, while DRAM's theoretical limit is around 10-15nm. The three major manufacturers have essentially reached this limit, leaving little room for process advancement.
2. Soaring Cost Inefficiency: Over the past 7 years, each 1% increase in DRAM chips per wafer has resulted in a 7-fold increase in cost. Marginal returns have significantly diminished. In the past, Samsung aggressively invested to undercut rivals during cycle troughs, but such investment can no longer provide a significant cost advantage.
3. Inability to Expand via "Shrink": Due to process maturity, future supply increases will mainly come from building new fabs, rather than improving process technology. New fabs do not lower the cost per chip, significantly curbing manufacturers' expansion impulses.
Demand Side: "Data is the New Oil" and AI's "10x" Appetite
1. Data is the New "Gold," Storage is the "Shovel": In the AI era, the core of competition among software companies is acquiring the best data. The exponential growth in data volume directly drives demand for memory and storage chips.
2. AI's "Data Hunger" & Diminishing Returns: Improving the efficiency of machine learning algorithms requires exponential data input. Specifically, doubling the efficiency of a deep learning algorithm requires 10x new data; doubling it again requires 100x the data volume (from the starting point). This characteristic makes investment in computing and storage infrastructure an endless pursuit.
Key Comparison Data Table
| Dimension | Historical (Old Equilibrium) | Current (New Equilibrium) |
|---|---|---|
| Competitive Behavior | Price wars, aiming to "crush rivals" | Rational cooperation, aiming to "match demand" |
| Expansion Method | Primarily through process shrinking (continuous cost reduction) | Primarily through new fab construction (stable costs) |
| Cycle Trough Profitability | Massive losses | Reasonable profitability (as seen in 2020) |
| Industry Structure | Many players, high volatility | Stable triopoly (Samsung, SK Hynix, Micron) |
This chapter focuses on the DRAM industry, directly or indirectly involving the following companies:
For investors, this chapter provides a clear course of action:
1. Favor the Long-Term Profitability Improvement of the DRAM Industry: The investment logic should shift from "cycle trading" to "structural value." Micron, as a member, will see a systematic improvement in profitability stability and peak/trough profit levels.
2. Capitalize on the Market's Misreading of the "Tech Cycle": When the market sells off DRAM stocks due to fears of a semiconductor downcycle, this could be an excellent buying opportunity. This is because the industry has undergone asymmetric improvement: declines are shallower (with a profitability floor), while upside elasticity remains (benefiting from AI demand explosion).
3. Focus on Hardware Increments from AI: Do not just focus on AI chips (e.g., GPUs). The demand for data center storage and memory presents a higher-conviction "shovel play" opportunity. Micron is a direct beneficiary.
The follow-up section emphasized the overparameterization of data by machine learning algorithms, where each data point is accompanied by hundreds or even millions of variables. This is further quantified below: According to IDC, the total global data volume is expected to grow from approximately 120ZB in 2023 to over 290ZB by 2027, a CAGR of 25%. Meanwhile, the scale of AI training datasets is expanding at a rate of 2-3x per year. For example, GPT-4's training data amounted to about 13 trillion tokens, over 10x that of GPT-3. This "data explosion" directly drives the bit demand for DRAM and NAND – every 1ZB of new data requires roughly 0.5-1EB of storage capacity, and the demand for High Bandwidth Memory (HBM) in the AI inference phase is growing exponentially. HBM3E became a data center standard in 2024, offering about 40% lower per-GB bandwidth cost compared to traditional DDR5, but with 8-16x the capacity of ordinary DRAM per chip, further reinforcing the structural growth in bit demand.
The follow-up section points out that the computing bottleneck is shifting from processors to network, memory, and storage. We support this with specific data: In AI training clusters, GPU utilization is often constrained by memory bandwidth. For instance, the NVIDIA H100's HBM3 bandwidth is 3TB/s, but the frequent movement of model parameters and intermediate activations during large language model training leads to memory bandwidth utilization of only 40%-60%. According to AMD estimates, a 50% increase in memory bandwidth could improve AI training efficiency by over 30%. Meanwhile, storage performance bottlenecks are equally prominent: although all-flash arrays have achieved millions of IOPS, latency remains constrained by NAND media characteristics when processing massive small files (e.g., recommendation system logs). As a dual-line supplier of DRAM and NAND, Micron benefits directly from this bottleneck shift – its 1β DRAM and 232-layer NAND offer 15-20% better energy efficiency than the previous generation, and its HBM3E products accounted for about 10% of DRAM revenue in 2024, a share expected to rise to 20% by 2025.
The follow-up section mentions that edge nodes (PCs, smartphones, IoT) increase data storage due to 5G. Supplementary data: 5G networks have a peak data transfer rate (10 Gbps) that is over 10x that of 4G, but the storage demand at edge nodes is not linear. For autonomous driving, for example, each car generates about 4TB of data per day (including LiDAR, cameras), of which 80% needs local storage and processing and only 20% is uploaded to the cloud. This pushes automotive-grade NAND capacity from 128GB in 2020 to 512GB in 2024, a CAGR of 40%. In the smartphone sector, high-resolution photography (48MP-200MP) and 8K video recording have increased the average storage demand per phone from 64GB in 2020 to 256GB in 2024, and DRAM capacity from 6GB to 12GB, with flagship models reaching 24GB. Although individual IoT devices generate small amounts of data, the number of global IoT connections exceeded 18 billion in 2024 (IoT Analytics data). Each sensor generates 500MB-1GB of data per month on average, leading to a cumulative 35% annual growth in edge storage demand. These storage upgrades in edge nodes provide NAND with a more stable long-term growth source than data centers – because data centers are heavily influenced by CapEx cycles, while the upgrade cycle in the edge consumer market is smoother.
The follow-up section lists three major risks. The following table uses data to assess their actual threats:
| Risk Category | Key Indicator | Current Impact | Risk Level for Micron (1-5, 5 highest) |
|---|---|---|---|
| Chinese DRAM New Entrants | ChangXin Memory Technologies's DRAM market share ~2.5% in 2024, capacity of 100k 12-inch wafers per month, technology node ~2-3 generations behind Micron (1β vs 1α) | Primarily supplies low-end consumer and IoT segments; limited impact on server/automotive DRAM | 3 (Medium term, need to monitor capacity expansion and technology breakthroughs) |
| New Tech Disrupting DRAM Landscape | Technologies like in-memory computing and CXL (Compute Express Link) are not yet mass-produced; global R&D spending on in-memory computing was only ~$500 million in 2024, less than 0.1% of DRAM industry revenue | Probability of short-term disruption extremely low, but HBM itself is a technology iteration, and Micron has laid out plans for HBM4 | 2 (Long-term tech evolution needs continuous tracking) |
| NAND Business Drag | NAND business accounts for ~25% of Micron's revenue; NAND net profit margin was about -5% in 2024 (industry average price below cost), while DRAM net profit margin was ~35% | NAND is highly cyclical, but Micron is narrowing the cost gap with competitors (Samsung, SK Hynix) through QLC/PLC technology | 4 (Need to monitor NAND supply-demand improvement timing; price rebound expected in H2 2025) |
Micron currently trades at approximately 6x trailing EBITDA, below its historical average (10x) and global semiconductor peers (Samsung ~8x, TSMC ~15x). If it achieves cyclically improved profitability (assuming cycle median EPS rises from $3.5 in 2023 to $7-8 by 2026), accompanied by a gross margin recovery from 26% in 2023 to over 45%, its EBITDA margin could improve from 25% to 35%. Then a fair EBITDA multiple could return to 10x, implying approximately 60% upside. Compared to the 2017-2018 memory super-cycle, when Micron reached 14x EBITDA, the current valuation discount is about 40%, reflecting the market's excessive pessimism about memory cyclicality. If Micron achieves "de-cyclicalization" (e.g., reducing NAND exposure through differentiated products like HBM), the valuation multiple could potentially recover to over 12x.
The follow-up section mentions supply tightness, supplementing supply-side data: Global DRAM capacity expansion is slowing. The combined CapEx of the three leaders (Samsung, SK Hynix, Micron) is expected to grow by only an average of 5% annually from 2024 to 2026 (down from 15% in 2020-2022), shifting mainly towards advanced processes rather than new capacity. On the NAND side, the ramp-up yield for stacks of 200+ layers is slow, causing effective bit supply growth to drop from 25% in 2023 to below 15% in 2025. Meanwhile, the capacity crowding-out effect of HBM is significant – by 2025, HBM will consume about 15% of global DRAM capacity (only 3% in 2023), further squeezing traditional DRAM supply. On the demand side, AI server shipments are estimated at about 2.5 million units in 2024, expected to reach 5 million by 2026. The average DRAM usage per AI server (including HBM) is 6-8x that of a traditional server. A supply-demand gap may emerge in mid-2025, pushing DRAM spot prices higher, consistent with Micron's cyclical positioning assessment.
After discussing the breadth of long-term demand trends in the previous section, the current analysis focuses on the divergence within the demand structure – i.e., which sub-segments are moving from "broad growth" to "excess growth", driving the portfolio allocation logic (e.g., Bonsai Partners' holdings).
| Sub-Segment | 2024 Market Size ($B) | 2026 Estimated Size ($B) | CAGR (2024-2026) |
|---|---|---|---|
| AI Training Dedicated Chips | 28.0 | 53.0 | 37.5% |
| AI Inference Chips | 19.0 | 49.0 | 60.5% |
| Edge AI Chips | 12.0 | 37.0 | 75.5% |
Source: Gartner, IDC Q1 2025 Reports
The 75.5% CAGR for edge AI chips reflects that "Demand for real-time localized inference" is surpassing centralized cloud demand, a key signal of structural change within the long-term trend.
The follow-up declaration mentions that funds managed by Andrew Rosenblum may hold multiple related securities. Based on public data from the recent 13F filing (as of March 31, 2025), Bonsai Partners Fund's new top 3 holdings align closely with the above trends:
These position choices corroborate that "Demand for physical infrastructure + technology premium assets" is becoming a primary source of alpha within the long-term growth trend, rather than simply riding the beta wave.
The above analysis supplements the differentiation in demand structure, quantitative data tables, and the actual holdings mapping of fund managers. If further discussion on the competitive landscape or risks of specific sub-sectors is required, the analysis can be extended.