Kospi Loses Its Memory: Samsung, SK Hynix Drag Index Down 5% as China's CXMT Looms 🧠

South Korea's KOSPI fell nearly 5% to 6,100 in Tuesday morning trading, extending a 3.7% slide from Monday and leaving the benchmark 10.1% lower over five days. The Korea Composite Stock Price Index remains up 44.89% for 2026 despite the pullback. Samsung Electronics and SK Hynix, which together account for more than half the index by market value, each fell roughly 5% by 9:13 a.m. in Seoul, and foreign investors sold a net 341.4 billion won of shares while individuals and institutions bought. The KOSPI was still down 4.06% at 9:49 a.m. in Seoul as Kiwoom Securities researcher Han Ji-young told clients he expected dip buying to spark a rebound during the session.

The selloff followed a weekend report that ChangXin Memory Technologies (CXMT), China's largest memory maker, had made progress on a denser 4F² chip design that TrendForce estimates could lift memory density by 30% to 50%. CXMT aims to ship server memory built on the new design by year-end, a higher-value market where Samsung and SK Hynix compete directly. In US trading overnight, Micron fell 3.9% and Sandisk 6%, according to Bloomberg data. Monday's slide also reflected foreign selling and the near-completion of chipmaker share buybacks, SBS News reported.

CXMT held about 8% of global DRAM revenue in the first quarter, per Counterpoint Research, with Samsung leading at 38%, SK Hynix at 29% and Micron at 22%. A Korea Times report noted that CXMT still struggles to stabilize yields on high-bandwidth memory and that Samsung and SK Hynix already sample the newer HBM4E generation. Korean chip stocks have previously reacted sharply to CXMT developments; the KOSPI fell more than 8% and triggered a circuit breaker after the company's July debut in Shanghai. Samsung and SK Hynix pushed the KOSPI past 9,000 in June, and the index now trades more than 30% below that level.