Why Did SanDisk Stock Jump?
SanDisk (SNDK) stock jumped 11.0% on Friday, September 18, 2026, its last trading day before joining the S&P 100. By the September 30 close of $1,739.89, the shares were about 3% below their September 18 close. SanDisk’s last quarterly report came in early August, so the jump did not follow new results. So what drove it, and what does the price assume now?
SanDisk Stock Jumped On The Last Trading Day Before Joining The S&P 100
SanDisk’s jump came on the last trading day before its S&P 100 membership took effect, not after new results. S&P Dow Jones Indices announced on September 4, 2026, that SanDisk would join the S&P 100 before the open on Monday, September 21, and funds that track the index generally buy at the prior session’s close. The S&P 500 rose only 0.2% on September 18. Seagate (+6.9%), Western Digital (+4.1%), and Micron (+3.9%) also rose, so part of SanDisk’s gain came with its whole group.
The jump came at the end of an uneven week. SanDisk shares fell 5.0% on September 14, 2026, as investors questioned how much longer spending on AI infrastructure could keep rising. The shares then rose 6.2% on September 17. Joining an index answers none of those doubts, because SanDisk earns no more from it. The share price now appears to assume that SanDisk’s data center sales keep growing and its chip prices stay high.
Is Demand For SanDisk’s AI Storage Still Growing?
Yes. SanDisk’s data center sales are still growing, and they made up about a third of its revenue in fiscal Q4 2026. Management says each step of AI work relies on data storage, including its high-capacity enterprise SSDs. Data center revenue was $2,977 million that quarter, out of $8,965 million in total. Data center revenue rose 103% from the quarter before.
In its fiscal Q4 2026 call, management said customer demand was growing faster than SanDisk’s supply. Management expects to keep rationing its chips to customers beyond calendar 2027. The index addition changed none of this. SanDisk’s chip prices are less settled than its demand.
SanDisk’s Recent Growth Came Mostly From Higher Flash Prices
SanDisk’s recent growth came mostly from higher prices. SanDisk sells NAND flash, a type of memory chip used for storage. Management said about two-thirds of the revenue gain from fiscal Q3 to fiscal Q4 2026 came from higher prices.
SanDisk kept 56.5% of its revenue as net profit in fiscal 2026 (the twelve months ended July 3, 2026), its highest in at least four fiscal years. The same twelve-month measure a year earlier was a loss equal to 22% of revenue. As of September 30, 2026, the stock traded at 22.4 times its trailing twelve-month earnings, close to the S&P 500’s 21.7. That multiple looks ordinary only while the net margin stays this high. If chip prices fall, you would pay the same share price for a smaller profit.
SanDisk has shielded some of its sales from falling prices. It has signed multi-year supply deals in which the variable part of the price has floors and ceilings. Management expects those deals to cover more than half of its chip output in fiscal 2027. Prices on the rest of SanDisk’s sales rise and fall with the market.
Gross margin, a different measure from net margin, is the share of revenue left after the cost of making the chips. Management’s guidance for fiscal Q1 2027 is an adjusted gross margin of 83% to 85%. SanDisk reported 84.6% on the same measure for fiscal Q4 2026. The 84% midpoint of that range sits just below the fiscal Q4 result, so management is guiding to margins that hold roughly flat rather than keep rising.
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