Samsung Electronics closes down 9.48% at 210,000 won on Thursday, and SK Hynix loses 11.06%, and the two together make up more than half of the Kospi’s market value, so the index does the arithmetic: down 7.57% to 5,554.22, its lowest close since April 7, after sliding as much as 9.29% intraday. Trading halted for 20 minutes at 12:38 p.m. in Seoul, the tenth Kospi circuit breaker this year, and it is the seventh straight losing session.

The explanation on offer has two halves. U.S. September CPI came in at 3.7% versus 3.6% expected, fueling bets on another Fed rate hike, and the Philadelphia Semiconductor Index had already fallen 4.3% overnight on doubts about whether AI infrastructure spending pays off. Foreign investors sold a net 2.9 trillion won. Japan’s Nikkei 225 dropped 4.9%, and Kioxia fell 12.3%. I can’t tell you how much of this was rates and how much was AI doubt, and I distrust any outlet that says it can, because both stories were already in the tape before Thursday.

Rates matter more for AI hardware than for most sectors because so much of the buildout is financed. When I wrote about Nvidia’s $500 billion vendor-financing deal in August, I worried about how much of the cycle depends on cheap money, and a rate-hike bet is the version of that worry that shows up in prices.

What makes the day odd is the data from the other side of the chain. A day earlier, ASML said its capacity won’t meet demand in 2027 or 2028, and TSMC reports the same day that it sees no sign of a slowdown. The question isn’t orders. The price investors will pay for those orders is.

Memory is where Korea’s exposure sits. Earlier this week I wrote about CXMT’s unverified 4F² DRAM claim and a Kospi drop of about 7%, and SK Hynix is the name carrying the HBM story; I covered its $4 billion Indiana packaging plant in August. A market that can take 11% off that stock in a session is the market funding the plan.

Sources

Reuters, South Korea’s KOSPI closes at 6-month low as chipmakers slump on AI worries, October 15, 2026
Firstpost, Why South Korea’s stock market crashed 7.6% as AI fears collide with US inflation, October 15, 2026
TradingKey, Japan and South Korea Stocks Slump as Kospi Closes Down 7.57%, October 15, 2026
AD HOC NEWS, KOSPI closes 7.6 percent lower as chip rout deepens, October 15, 2026
IBTimes Australia, Kospi Rebounds Nearly 2.5% After Seven-Day Rout, October 16, 2026