South Korea’s benchmark KOSPI index fell 9.99% on June 23, closing at 8,204 points in its steepest single-day decline in over three months. The sell-off was severe enough to trigger circuit breakers, halting trading for 20 minutes while the market tried to catch its breath.
The culprits were familiar names. SK Hynix and Samsung Electronics, the twin pillars of South Korea’s memory chip industry and the primary beneficiaries of the global AI spending boom, each dropped more than 12% on the day. When those two companies together account for roughly 40-50% of the entire KOSPI’s market capitalization, their bad days become everyone’s bad days.
A rally that doubled, then stumbled
The KOSPI had surged more than 100% year-to-date by June 2026, peaking above 9,000 points. The rally was almost entirely driven by demand for advanced memory products used in AI data centers and training infrastructure, which sent SK Hynix and Samsung’s valuations soaring, dragging the entire KOSPI along for the ride.
The Kospi 200 Volatility Index, South Korea’s equivalent of Wall Street’s VIX “fear gauge,” spiked to around 75. Normal readings hover around 20.
