SanDisk (NASDAQ: SNDK) fell about 14% on Tuesday to hover just above the $1,000 mark — its third straight double-digit down day and roughly a 31% slide in three sessions. That's a brutal reversal for what was the S&P 500's single best stock of the first half of 2026.

Some context on how far this ran: SanDisk peaked at an all-time high of $2,354.39 on June 22 after a ~726% first-half surge. It's now worth less than half that. When a stock goes vertical on the AI trade, the air pocket on the way down is just as violent.

So what's actually driving it?

• China memory fear, with a real number. Chinese memory champion CXMT just pulled off a blockbuster Shanghai listing, raising more than $8 billion in fresh cash to build fabs and expand output. Flash memory is a commodity — more Chinese supply is a direct threat to NAND contract prices and the fat margins the whole group has enjoyed.
• This is NOT an earnings crash. SanDisk hasn't reported yet — fiscal Q4/FY26 lands Aug 5, with an investor day Aug 13. So the drop is a positioning unwind on softening NAND wafer prices and oversupply worries, turbo-charged by the broader AI-chip selloff and a crowded, retail-heavy shareholder base heading for the exit at once.

The ripple: this isn't a SanDisk-only story. Because NAND is a commodity, the same China-glut fear hits every memory maker — Micron (MU), SK Hynix and Kioxia — whose per-bit margins compress the moment contract prices roll over. That's why the memory names sold off together, not in isolation.

The one thing that flips it: Aug 5. If SanDisk's guidance shows NAND pricing and margins holding up into the data-center build-out, this China-supply scare can unwind as fast as it arrived. If management flags the margin pressure the market is already bracing for, watch whether $1,000 holds — lose that line and the momentum crowd has no obvious floor beneath it.

As of the Jul 28 US close (Wed Jul 29, ~10:50 AM IST). Sources: The Motley Fool, Yahoo Finance. For discussion and education only — not investment advice. Verify before acting.