South Korea’s KOSPI fell nearly 5% to 6,100 on Tuesday morning as Chinese chip progress hit Samsung and SK Hynix. The two chipmakers hold more than half the index by market value.

The Korea Composite Stock Price Index (KOSPI) extends a 3.7% slide on Monday and sits 10.1% lower over five days. Even so, it remains up 44.89% for 2026.

Why Is a Chinese Memory Maker Shaking Korean Stocks?

ChangXin Memory Technologies (CXMT), China’s largest memory maker, reported progress over the weekend on a denser 4F² chip design.

It’s been reported that TrendForce estimates the design could lift memory density by 30% to 50%. CXMT aims to ship server memory built on it by year-end, a higher-value market where Samsung and SK Hynix compete.

Samsung Electronics and SK Hynix each fell roughly 5% by 9:13 a.m. in Seoul. Foreign investors sold a net 341.4 billion won of shares, while individuals and institutions bought.

The Kospi has opened nearly 5% down. Image: Trading View

Micron fell 3.9% and Sandisk 6% in US trading overnight, Bloomberg data showed.

Monday’s slide also reflected foreign selling and the near-completion of chipmaker share buybacks, SBS News reported.

Does CXMT’s Progress Justify a Selloff This Size?

A Korea Times report says CXMT still struggles to stabilize yields on high-bandwidth memory. Samsung and SK Hynix already sample the newer HBM4E generation.

CXMT held about 8% of global DRAM revenue in the first quarter, per Counterpoint Research. Samsung led with 38%, SK Hynix followed with 29%, and Micron held 22%.

Korean chip stocks have flinched at CXMT before. The KOSPI fell more than 8% and triggered a circuit breaker after the company’s July debut in Shanghai.

Kiwoom Securities researcher Han Ji-young expected dip buying to spark a rebound during the session. The index was still down 4.06% at 9:49 a.m. in Seoul.

Samsung and SK Hynix pushed the KOSPI past 9,000 in June. The index now trades more than 30% below that mark.

Because two stocks hold half the benchmark, doubts about their DRAM dominance now move the whole market.

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