Samsung and SK Hynix led a brutal sell-off as investors questioned whether massive AI spending will ever pay off
South Korea’s stock market just had the kind of day that makes portfolio apps feel like horror films. On October 15, 2026, the KOSPI index fell 7.57% to close at 5,554.22, its lowest finish since April.
The culprit was a growing crisis of faith in artificial intelligence. Specifically, investors are asking whether the enormous sums being poured into AI infrastructure will ever turn a profit.
The damage was concentrated where you would expect. Samsung Electronics dropped about 9.5% on the day, while SK Hynix slid approximately 11%.
And these were not one-off stumbles. SK Hynix now sits roughly 35% below its peak value, while Samsung is down roughly 22% from its high.
The index itself has fared even worse. The KOSPI peaked at 9,386 in June 2026 and has since fallen approximately 40% from that level.
The selling was severe enough to trigger circuit breaker interventions on multiple trading days, including October 15. Circuit breakers are automatic pauses that halt trading when prices fall too fast.
Several forces converged at once. First came higher-than-expected US inflation data. Hotter inflation raises the odds that interest rates stay elevated or climb further, which is bad news for growth stocks priced on distant future earnings.
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Second, signs of financial distress began surfacing across AI-related sectors. Third, major AI firms including OpenAI and Anthropic issued revenue forecasts that disappointed the market.
Foreign investors also headed for the exits, selling billions of dollars in Korean shares during October 2026.
The pessimism did not stay confined to established giants. On October 20, 2026, AI-related firm Elice made its market debut, and its shares promptly plunged 32%.
Earlier in 2026, the KOSPI surged 116%, a rally driven heavily by enthusiasm for AI and the semiconductors that power it. Even after the recent carnage, the index is still up about 30% year-to-date.
The clearest lesson is about concentration risk. A market that leans heavily on a handful of semiconductor companies is effectively a leveraged bet on a single theme, which is exactly what the October sell-off exposed.
The deeper question is whether this is a healthy correction or the start of a broader reassessment of AI economics. The answer likely hinges on whether the revenue from AI services eventually catches up with the spending on AI hardware, and disappointing forecasts from OpenAI and Anthropic did nothing to settle those nerves.
Foreign fund flows are another variable worth tracking. Continued selling by overseas investors would keep weighing on Korean equities.