AI chip stocks in South Korea and Japan tumble after US semiconductor selloff

The Kospi closed down approximately 5.5% as Samsung, SK Hynix and Kioxia followed Wall Street's chip slide lower

Wall Street’s chip stocks had a bad day. On October 13, 2026, Asia inherited the hangover.

AI-related shares in South Korea and Japan slid sharply after US semiconductor names sold off in the prior session. South Korea’s Kospi fell as much as 7% intraday before closing down approximately 5.5%.

The damage in Korea was concentrated in exactly the place you would expect: memory chips.

Samsung Electronics and SK Hynix both fell by around 7-10% during the session. The two companies account for nearly half of the Kospi’s market capitalization.

The selloff pushed the Kospi to its lowest level since late July 2026. The index had peaked earlier in the year, so this was a fall from a considerable height.

Foreign investors sold more than $6.3 billion worth of Kospi shares in October 2026.

Japan did not escape. The Nikkei 225 lost more than 2-3%, dragged lower by chip-related names.

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Kioxia led the decline, with its shares falling about 12-13%.

The trigger came from the US. The Philadelphia Semiconductor Index, known by its ticker .SOX, posted its sixth straight decline, with an approximate 1.5% drop in a single session.

Recent US consumer price index data showed inflation running faster than expected. That shifted thinking around the possibility of rate hikes and weighed on investor sentiment.

The second concern is about the money behind the AI buildout itself. Weakness in CoreWeave’s bonds raised specific worries about how AI infrastructure is being funded.

The concentration issue in Korea deserves particular attention. An index where two companies make up nearly half the value is effectively a leveraged bet on memory chips.

Competition is another factor in the mix. Intensifying rivalry, particularly from Chinese firms, could make investors more cautious about how much they are willing to pay for future AI-driven earnings.

The sixth straight decline in the SOX, the October foreign outflows from Korea, and the next round of US inflation data will all help determine whether this was a sharp correction or the start of a longer reassessment of the AI story.