South Korea's KOSPI Crashes 8% and Triggers Circuit Breaker as Global Tech Selloff Deepens

South Korea's KOSPI index plunged 8% on October 15, triggering a market-wide circuit breaker that halted all stock and program trading for 20 minutes, as a global technology selloff accelerated across Asian markets. The decline marked the seventh consecutive losing session for the index, pushing it to its lowest levels since late July and erasing approximately 1,186 trillion won, or roughly $880 billion, in market value over those seven sessions, a cumulative drop of 21%.

Semiconductor heavyweights drove the losses. Samsung Electronics fell more than 11% and SK Hynix sank around 12%, with investors questioning whether the AI infrastructure spending boom that had made the KOSPI the world's best-performing major market in the first half of 2026 could be sustained at elevated interest rates. Earlier in the session, before losses widened to 8%, the Korea Exchange had already activated a sell-side sidecar mechanism, temporarily suspending program sell orders for five minutes, as rapid selling pressure mounted.

The catalyst was hotter-than-expected U.S. September CPI data showing headline inflation at 3.7% year-over-year, which sent the 10-year Treasury yield spiking above 5.3% before it pulled back to around 5.189%. That report hit Wall Street on October 14, where the Nasdaq Composite dropped 511.51 points, or 1.88%, to 26,692.87 and the S&P 500 fell 86.51 points, or 1.11%, to 7,718.94. AI infrastructure names bore the sharpest losses: CoreWeave fell 15.46% to $65.78 following a Gartner warning that 80% of neoclouds could disappear by 2030, while DigitalOcean dropped 14.85%, Dell Technologies declined 11.34% after a Barclays downgrade, and Oracle fell roughly 9%. AI infrastructure stocks collectively erased around $80 billion in U.S. market value in a single session.

The rout spread through Asia. Japan's Nikkei 225 tumbled more than 3%, with flash-memory maker Kioxia Holdings falling 8% to 10% and SoftBank Group dropping 6% to 7%. Concerns included not only higher-for-longer U.S. rates and elevated oil prices but also rising competitive supply in the memory chip market. In India, foreign institutional investors were net sellers of roughly 1,857 crore rupees on October 14, though domestic institutions absorbed more than 2,670 crore rupees in net purchases.