Seoul's Kospi index plunged as much as 12.6% on July 29, 2026, capping a two-day sell-off that erased more than 40% of the index's value from its peak reached just over a month earlier. The rout dragged the Kospi to its lowest level since early April and followed a near-11% decline on July 28, the index's worst single-day session in roughly five months. Japan's Nikkei fell 1.5% on the 29th, and TSMC shares dropped 3% in Taipei, but the epicenter of the crisis was South Korea, where two companies dominate the market.

SK Hynix and Samsung Electronics together account for more than half the Kospi's market capitalization. On July 29, SK Hynix shares fell as much as 16% while Samsung traded nearly 10% lower, a day after both had each dropped more than 13% during the July 28 session. Bloomberg reported that SK Hynix had plunged as much as 20% intraday on the 28th before the earnings release.

The trigger was SK Hynix's Q2 2026 earnings, released at 9:00 AM KST on July 29. The company posted record results: revenue of 79.32 trillion won (approximately $54.55 billion), up 257% year-over-year, and operating profit of 60.5426 trillion won, with net profit reaching 93.9226 trillion won, a 557% jump from the prior-year quarter. SK Hynix characterized the results as record-breaking. The net profit figure was boosted by investment gains.

None of it was enough. Analyst consensus had pegged Q2 revenue at 84 trillion won, and both profit and revenue missed estimates. More critically, investors were looking for additional catalysts around long-term agreements and shareholder returns, and the earnings release did not deliver them. The sell-off had in fact begun the day before the results were published, as Reuters reported that investors were already questioning the lofty valuations of Asian semiconductor stocks.

The rout fits a pattern that had been building for weeks. On July 8, the Kospi had already fallen 5.35% (409.52 points) to close at 7,246.79, down 20% from its June record close, driven by sharp swings in chipmaker stocks. SK Hynix completed a Nasdaq listing debut valued at $29 billion around July 13, potentially the largest-ever first-time share sale by a foreign company. Its ADRs fell 9.3% on their second trading day, and the AI-fueled stock rout in South Korea spilled over into the US market via those ADRs. As of July 28, a broad measure of Asian stocks had slid 10% from its June peak and was heading for correction territory.

Several converging pressures deepened the dislocation. Bloomberg reported that signs of progress in China's advanced chipmaking compounded investor worries about the sustainability of AI spending, while concerns about AI-related debt levels further rattled the sector. On Wall Street, US chip stocks Intel, AMD, Sandisk, Western Digital, and Seagate Technology all fell on July 28. The contagion was broad but selective: Apple's stock briefly rose above the $5 trillion valuation mark that same day, making it the second company ever to reach that milestone. Brent crude oil climbed to $87.14 a barrel, up about 3.6%.

The broader context here is a market that had priced in perfection across the AI semiconductor supply chain and is now repricing rapidly. SK Hynix's Q2 numbers, taken in isolation, are extraordinary: sequential growth from Q1 revenue of 52.5763 trillion won and operating profit of 37.6103 trillion won, with net profit nearly tripling from Q1's 40.3459 trillion won. A 557% year-over-year profit increase at a company of this scale is not a marginal event. Yet the market reaction makes clear that expectations had outrun even these numbers. The miss against the 84 trillion won consensus is part of the story, but the deeper frustration was the absence of forward-looking signals on long-term supply agreements and capital return commitments.

Two structural vulnerabilities amplified the damage. The Kospi's extreme concentration in SK Hynix and Samsung means that any idiosyncratic shock to either name becomes a systemic event for the entire index. And SK Hynix's recent Nasdaq listing, intended to broaden its investor base to AI-focused US capital, has created a new transmission channel for volatility to flow between Seoul and New York in both directions.

The China factor adds a geopolitical dimension. Progress in Chinese advanced chipmaking directly threatens the competitive moat that Korean memory and logic chipmakers have relied on, and investors are now pricing in a scenario where AI infrastructure spending, rather than accelerating indefinitely, may face saturation, margin compression, or both. The AI debt jitters reported by Bloomberg suggest that the financing underpinnings of the AI capex cycle are themselves being scrutinized.

Whether this sell-off marks a temporary repricing or a more durable reassessment of the AI semiconductor trade will depend on several factors the current facts cannot yet illuminate: the pace of HBM (high-bandwidth memory) demand from hyperscaler customers, the trajectory of Chinese domestic chip capacity, and whether SK Hynix and Samsung can articulate forward guidance that rebuilds confidence in the sustainability of their earnings trajectory. For now, the market has delivered an unambiguous verdict: record profits, in this cycle, are not sufficient.