CXMT Memory Advance Hits Samsung and SK Hynix as KOSPI Slides Nearly 5%

On Tuesday morning, South Korea's KOSPI slipped nearly 5% to 6,100, with Samsung and SK Hynix under pressure from Chinese chip advances. The two chipmakers account for more than half the index's market value.

The Korea Composite Stock Price Index (KOSPI) carried Monday's 3.7% decline further and was 10.1% down across five days. Despite that, its 2026 gain still stands at 44.89%.

Why Is a Chinese Memory Maker Rattling Korean Equities?

Over the weekend, ChangXin Memory Technologies (CXMT), China's biggest memory producer, said it had made headway on a denser 4F² chip design.

TrendForce, according to reports, estimates the design could boost memory density by 30% to 50%. CXMT is targeting year-end shipment of server memory built around it, a higher-value market in which Samsung and SK Hynix compete.

At 9:13 a.m. in Seoul, Samsung Electronics and SK Hynix were each down about 5%. Individuals and institutions purchased shares, while foreign investors made net sales of 341.4 billion won.

Overnight in the US, Micron slid 3.9% and Sandisk declined 6%, according to Bloomberg data.

SBS News reported that Monday's drop was also tied to foreign selling and chipmakers nearly finishing their share buybacks.

Is a Drop of This Magnitude Justified by CXMT's Progress?

CXMT continues to have trouble stabilizing yields on high-bandwidth memory, according to a Korea Times report. The newer HBM4E generation is already being sampled by Samsung and SK Hynix.

Counterpoint Research puts CXMT at about 8% of worldwide DRAM revenue in the first quarter. Samsung was first with 38%, SK Hynix came next with 29%, and Micron had 22%.

CXMT has spooked Korean chip stocks in the past. When the company debuted in Shanghai in July, the KOSPI lost more than 8% and a circuit breaker was triggered.

Han Ji-young, a researcher at Kiwoom Securities, thought buying the dip would trigger a rebound during the session. At 9:49 a.m. in Seoul, the index was still off 4.06%.

In June, Samsung and SK Hynix drove the KOSPI above 9,000. At present, the index trades more than 30% under that level.

Since two stocks represent half of the benchmark, uncertainty about their DRAM dominance now shifts the entire market.