A decline of more than 8% hit the KOSPI during Thursday's trading, steep enough to trigger circuit breakers across the exchange, as technology stocks bore the brunt of a broader sell-off tied to inflation data that exceeded analyst projections and growing investor uncertainty over the long-term payoff from artificial intelligence investment.

South Korea's KOSPI index slid to 5,514.96 on Friday, a reading not seen since late July, reflecting a loss of 8.2% across the session. Taken together, a drop recorded in the most recent session pushed seven-day cumulative losses to 16.9%, with the broader three-month retreat now standing at 24.4%.

Declines in South Korean stocks ran deeper than those recorded across other prominent Asian exchanges. Selling pressure concentrated in semiconductor shares pulled Tokyo's Nikkei 225 down roughly 5%, with Taipei's Taiex shedding around 3.4% over the same stretch.

A halt to KOSPI trading, lasting 20 minutes, was triggered once the index held at least 8% beneath its prior closing level for a continuous minute. When sharp selling pressure builds across a market, a temporary halt — the circuit breaker — opens a pause in activity so that traders can take stock of conditions before any further transactions proceed.

For the exchange, a tenth circuit breaker of 2026 fired on Thursday — bringing the all-time total for such interventions to sixteen since the mechanism was first introduced. Trading activity had last been halted on the 29th of July.

September's U.S. consumer price index reading put annual inflation at 3.7%, a figure that came in above what economists had projected, and that result weighed on markets. Those data points fed into market expectations that the Federal Reserve would hold borrowing costs at their current level or push them even higher.

Overnight trading on the Nasdaq Composite ended with a 1.9% decline, pulling Wall Street into negative territory alongside broader market pressure. Six straight down days have now accumulated for the Philadelphia Semiconductor Index, with no winning session breaking the streak.

Shares in South Korea's top semiconductor companies drew persistent downward pressure from sellers. Shares in Samsung Electronics retreated 9.7%, with SK Hynix posting a steeper loss of 11.1%. Sanil Electric shed 16.9% of its value, while Samsung Electro-Mechanics and Hansol Technics posted respective retreats of 16.8% and 15.2%. Shares of Daeduck Electronics and IsuPetasys retreated by 15.1% and 14.9%, in that order.

Questions about whether AI infrastructure outlays can be sustained, combined with the rise of Chinese memory chipmaker ChangXin Memory Technologies as a competitive force, have put pressure on longer-established players across the semiconductor industry.

Compared with June — when enthusiasm around artificial intelligence lifted the KOSPI past the 9,000-point threshold — the index has since moved in the opposite direction. Trading roughly 40 percent beneath its 52-week peak of 9,385.59, the index has prompted a broader reassessment among investors of how technology stocks are priced, what semiconductor companies might report in upcoming earnings, and whether the wave of spending on artificial intelligence can hold its pace.