Micron and SanDisk Lead AI Chip Selloff as Seoul Markets Crash

A cascade that started in Seoul arrived in U.S. markets Tuesday, wiping double-digit percentages off memory-chip names in a single session. According to MarketWatch and corroborating reporting from 247 Wall St., SanDisk fell roughly 11% and Micron and Western Digital each slid around 10%, reversing off record highs after surging in 2026.

The proximate trigger was not an AI earnings miss or a hyperscaler demand cut. South Korea's KOSPI fell roughly 9-10%, tripping circuit breakers that halted trading, while Samsung Electronics dropped 12.31% and SK Hynix fell 12.47% in Seoul. Yahoo Finance reported that the crisis traced to a Monday briefing from Financial Supervisory Service Governor Lee Chan-jin, who said he wished he had done more to block the late-May launch of 16 single-stock leveraged ETFs tracking Samsung and SK Hynix. Those instruments reportedly held combined assets that swelled to roughly 14 trillion won (about $9.1 billion), with approximately 92% of holders being retail investors. When those structures started unwinding, the pressure spread globally.

The timing is uncomfortable. Micron is scheduled to report fiscal third-quarter 2026 results after the close on June 24. HBM capacity has reportedly been sold out through much of 2026 under multi-year hyperscaler agreements, and that supply scarcity is the central thesis behind the bull case for Micron and the broader memory trade. A single session's selloff does not disprove that thesis, but it puts the earnings call under unusual pressure to reaffirm it.

The honest caveat is that the selloff's mechanics tell you more about how fragile stretched valuations are than about whether AI data center orders have changed. SanDisk, which reportedly ran nearly 5,000% since its 2025 spin-off and was trading at a price-to-earnings ratio above 79, was always going to be vulnerable to a sharp de-risking event. What the reporting does not give you is clarity on whether the forced selling in Korean markets is finished, or how much of the move is genuine valuation reassessment versus contagion. Micron's forward guidance on HBM demand and second-half data center orders will be the first real signal about which way memory stocks go from here.