South Korea’s benchmark KOSPI index crashed 9.99 percent on June 23, closing at 8,203.84 after shedding 910.71 points, a one-day collapse so steep it triggered a market-wide circuit breaker that halted trading for 20 minutes. The plunge was led by the country’s two semiconductor giants and amounted to one of the sharpest single-session declines in years.
Samsung Electronics fell roughly 12.3 percent and SK Hynix about 12.5 percent, as foreign investors dumped a net 5.79 trillion won — around $3.8 billion — of Korean shares. The selling was severe enough to activate a sidecar mechanism that briefly suspended program trading after KOSPI 200 futures tumbled.
The immediate trigger came from overseas. A heavy overnight selloff in US technology stocks, combined with renewed worries that the Federal Reserve under new chair Kevin Warsh may raise rates again to curb inflation, hammered semiconductor sentiment across Asia. Compounding the damage, South Korea was left out of an upcoming MSCI review for inclusion in its Developed Markets index, removing a catalyst many investors had been positioning for.
The crash exposed how concentrated the Korean market has become. Together, Samsung and SK Hynix account for nearly half of the KOSPI’s total value — about 48 percent — and have contributed roughly 70 percent of the index’s gains in 2026. SK Hynix alone had climbed nearly 190 percent on the year before the drop, driven by insatiable demand for the high-bandwidth memory that powers AI data centers.
That concentration cuts both ways. The same names that drove the index to records on June 22 dragged it down the next session, and when sentiment turned, there was little to cushion the fall. Analysts framed the move less as a verdict on the companies’ fundamentals — both remain highly profitable — than as a sudden reassessment of how much future success was already baked into their prices.
For all the drama, the rout did not erase the year. Even after the 10 percent fall, the KOSPI remained up roughly 80 percent for 2026, ranking it among the world’s best-performing major equity benchmarks. On June 24 the index rebounded about 3 percent to 8,471, as bargain hunters returned and Asian tech shares steadied.
The episode is a reminder that this year’s AI-driven rally, however well-grounded in real demand, has produced valuations sensitive to every shift in interest-rate expectations and every headline out of Wall Street. With memory makers booked to capacity and AI spending still climbing, the long-term story remains intact — but June 23 showed how violently the market can reprice that story in the space of a morning.