KOSPI circuit breaker on October 15, 2026: Samsung fell 9.48% and SK hynix 11.06% as Asian chip stocks crashed

South Korea's KOSPI fell 7.57% to 5,554.22 on Thursday, October 15, 2026, after a circuit breaker stopped trading for 20 minutes, as memory-chip makers led a selloff across Asia. SK hynix closed down 11.06% at 1,262,000 won and Samsung Electronics 9.48% at 210,000 won. In Tokyo the Nikkei 225 lost 4.90%, its third-largest point drop on record, and Advantest fell 14.96%.

The selling followed the US session of October 14, when a hotter-than-expected inflation report and doubts about the financing of AI data centers pushed the Philadelphia Semiconductor index down 4.3%. Korean and Japanese chipmakers had already been falling for days on worries about Chinese memory competition.

How the session unfolded

The first headlines understated the day. In the opening minutes SK hynix was reported down 7% and Samsung down 7.3% at 215,000 won, and the Korea Exchange's notice that it had activated a sidecar on the KOSPI, which suspends program selling for five minutes, reached the MoveSurge news feed at 09:08:08 Seoul time. The decline deepened through the morning until the KOSPI's first-level circuit breaker triggered at 12:38 p.m. with the index down 8.00% at 5,528.05. Trading stopped for 20 minutes and resumed with a 10-minute call auction. It was the first circuit breaker since July 29 and the tenth of the year. The KOSDAQ had halted at about 12:23 p.m. and closed down 7.65% at 760.82.

Foreign investors sold a net 3.63 trillion won of KOSPI shares, their eighth straight day of net selling, while individuals and institutions were net buyers. The KOSPI's close was its lowest since April 7 and its seventh losing session in a row.

Tokyo

The Nikkei 225 fell 3,318.34 points to 64,425.95, its sixth straight loss, and the broader TOPIX lost 2.38%. Chip equipment and memory stocks took the most points off the index.

Why chip stocks crashed in Seoul and Tokyo

September US consumer prices rose 3.7% on the year against a 3.6% forecast, which raised the odds of another Federal Reserve rate increase; our report on the CPI release has the first-minute moves. Higher rates bear hardest on the companies whose growth depends on AI spending financed with debt, and the same day CoreWeave fell 15.46% as its bonds traded at distressed yields. For memory makers there was a second worry: China's CXMT said on October 10 it had made progress on a new DRAM design, and a Counterpoint forecast cited by CNBC put DRAM prices about 23% lower in 2028 than in 2027. SK hynix has tied part of its high-bandwidth memory output to multi-year customer agreements with prepayments, as our report on those agreements explains, and the forecast put a price on what buyers could pay once such contracts come up for renewal.

The next day

On Friday, October 16, the KOSPI rebounded 2.05% to 5,668.05, Samsung rose 2.62% to 215,500 won and SK hynix 0.79% to 1,272,000 won, and foreign investors turned net buyers. The Nikkei rose 1.39% to 65,324.29. The relief did not reach New York, where the Nasdaq fell 572.99 points that day as chip stocks slid again. Two months earlier the KOSPI had been surging to records on the same memory trade.