The S&P 500 has risen 28% in the past 12 months, while Nvidia has surged 73%. However, compared to the storage sector, these gains pale in comparison. SanDisk, priced at $34.61 a year ago, is now at $1,406.32, soaring 39 times.

This NAND flash memory manufacturer, which split from Western Digital just 14.5 months ago, is the strongest performing stock in the US market as of 2026, with a staggering 492% increase this year. Behind it, Micron, Seagate, and Western Digital have had YTD gains ranging from 124% to 492%, with the lowest performer still having increased by 23 times compared to Nvidia. The "shovel seller" label of the AI revolution is shifting from the GPU side to the memory side.

The most notable date is May 5th. On this day, SanDisk rose 11.98%, Micron increased by 11.06%, Western Digital was up 5.18%, and Seagate climbed 4.38%. Among the four US storage manufacturers, three reached new 52-week highs.

The catalysts were two financial reports and a supply story. On April 28, Seagate reported a 44% year-on-year revenue increase for Q3 FY26, with a record gross margin of 47%. CEO Dave Mosley said in the conference call, "AI has ushered Seagate into a new era of structural growth," with nearline exabyte capacity already allocated until 2027.

Two days later, SanDisk announced Q3 FY26 revenue of $5.95 billion, a 252% year-on-year increase, exceeding the upper guidance by $1.15 billion, with data center revenue up 645% year-on-year, nearly doubling quarter-on-quarter, and Q4 guidance expecting a further increase of 308% to 334% year-on-year. Coupled with Micron receiving a credit rating upgrade from Fitch, the entire sector soared on Monday.

But this is the surface. Looking at the four stocks individually, the idea of "all storage sector rising" is actually a misleading generalization. They are benefiting from three completely different supply stories, with vastly varying degrees of increases.

From a year-to-date perspective, SanDisk +492.43%, Seagate +180.46%, Western Digital +170.21%, Micron +124.40%, distributed across four completely different tiers. During the same period, the S&P 500 rose by 6.04%, and Nvidia increased by 5.37%. The latter even dropped 7.82% in the past five days. The label of "the first beneficiaries of AI" is shifting: the GPU story driven by large model training has completed its valuation expansion cycle in the past year, and money is beginning to flow downstream, into the memory and storage needed to support AI workloads.

This shift in tiers is not even. It is stratified along the medium attributes.

The numbers from the most recent quarter's financial reports make this stratification very clear. SanDisk reported a 252% year-on-year revenue increase on the NAND side, Micron saw a 196% increase on the DRAM/HBM side, while Western Digital and Seagate both had around 44-45% year-on-year revenue growth on the HDD side. NAND and DRAM are in the explosive tier, while HDD is in a steady growth tier, with a 4 to 5 times difference between the two.

Gross margin stratification is even more exaggerated. Micron's Q2 FY26 gross margin was 74.4%. This is an extreme figure for a chip manufacturer, meaning that for every $100 of DRAM and HBM sold, $74 goes to the profit statement. Seagate's 47% gross margin, while a historical high for itself, lags behind DRAM manufacturers by an order of magnitude. This is due to differences in supply structure. HBM capacity is concentrated among three companies (SK Hynix, Samsung, Micron), and all are sold under long-term contracts until the end of 2026. HDD capacity is evenly distributed between Seagate and Western Digital, giving relatively dispersed pricing negotiation power.

The pricing side provides the same signal.

According to TrendForce, on February 2, the 1Q26 memory contract price guidance was adjusted, indicating that PC DRAM rose 100% quarter-on-quarter, server DRAM about 90%, and server LPDDR4X/5X about 90%, with all three types of DRAM reaching record highs. On the NAND Flash side, enterprise SSDs rose 53% to 58%, with NAND overall increasing by 55% to 60%, only a little more than half of DRAM's increase.

This is a scissor gap that explains everything. AI servers require both NAND and DRAM, but they need bandwidth (HBM) and capacity density (DDR5, LPDDR5X) even more. The supply-demand gap on the DRAM side is much larger than that on the NAND side. Micron's CEO succinctly stated during the Q2 FY26 earnings call, "We're sold out for 2026," summarizing the supply story clearly. HBM4 36GB 12H has already been mass-produced for Nvidia's Vera Rubin platform, and the full-year capital expenditure for FY26 has been raised from $20 billion to $25 billion, aiming for another tier in 2027.

Among the four manufacturers, SanDisk is the most noteworthy to look at individually.

SanDisk became independent from Western Digital on February 24, 2025, and was listed on Nasdaq. It opened at $52 on the first trading day, closing at $48.60, with a market value of approximately $7.2 billion. On the same day, Western Digital closed at $49.02, with a market value of about $16.9 billion. On the day of the split, Western Digital's size was 2.3 times that of SanDisk.

Today, 14.5 months later, SanDisk has a market value of $208.3 billion, while Western Digital has a market value of $160.4 billion. SanDisk is now 1.3 times the value of Western Digital. Such an inversion is rare in the history of large corporate splits. In most split cases, subsidiaries still spend the first year rebuilding investor relations and typically take 3 to 5 years to catch up to the parent company's market value. SanDisk achieved this in just 14.5 months.

The reason is that it was split at the most opportune time. When Western Digital decided to split in 2024, the reason given was "NAND and HDD are in different capital cycles, and separating them leads to clearer valuations." This judgment was later validated by the market: after becoming independent, SanDisk focused solely on NAND, coinciding perfectly with the explosive demand for enterprise-level SSDs from AI data centers. Western Digital, focusing exclusively on HDD, benefited from the structural growth of cloud storage archiving. The two companies, separated, correspond to different narratives. If they hadn't split, a single company would have housed two completely different supply cycles, and the capital market would have used a more conservative valuation multiple, placing it in the middle.

Bernstein raised SanDisk's target price from $1,250 to $1,700 on May 4, citing the visibility of the data center SSD business. SanDisk's financial report revealed that it had signed five long-term contracts, received $11 billion in financial guarantees, and locked in over one-third of NAND bits for fiscal year 2027. This is a sector traditionally treated according to commodity cycles, but has now seen the emergence of a structure resembling advanced process wafer foundry with "long-term contracts + client prepayments."

Overall, money is flowing from the GPU side to the memory side; DRAM is the true alpha in this round, HDD is a long-term structural growth playing to a different rhythm, and SanDisk, which became independent just 15 months ago, has surpassed its parent company Western Digital in market value through its NAND data center line.

On the same trading day, May 5, Nvidia fell 1.03%, TSMC declined 1.79%, while SanDisk rose 11.98%. All considered "beneficiaries of AI," the market is already voting with its feet, distinguishing which segment of supply is the most scarce.

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