South Korea'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 (the total value of all shares listed on the exchange). 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% during the trading day on the 28th, before the company released its earnings.

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

None of it was enough. Analysts had expected Q2 revenue of about 84 trillion won, and both profit and revenue fell short of those estimates. More importantly, investors were looking for positive signals about long-term supply agreements and plans to return money to shareholders, and the earnings release delivered neither. The sell-off had actually started the day before the results came out, as Reuters reported that investors were already questioning whether Asian semiconductor stocks were valued too highly.

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 (a debut sale of shares on the US tech exchange) valued at $29 billion around July 13, potentially the largest-ever first-time share sale by a foreign company. Its ADRs (American Depositary Receipts — certificates that let US investors buy foreign shares) fell 9.3% on their second trading day, and the stock turmoil in South Korea spilled into the US market through those ADRs. As of July 28, a broad measure of Asian stocks had slid 10% from its June peak and was heading toward correction territory — a term used when an index falls 10% or more from a recent high.

Several converging pressures deepened the sell-off. Bloomberg reported that signs of progress in China's advanced chipmaking added to investor worries about whether AI spending could keep growing at its current pace, 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 effects were 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 on their own, 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 minor 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 shock specific to either company becomes a system-wide event for the entire index — think of it as a portfolio where two holdings are so large that a bad day for either one moves everything. And SK Hynix's recent Nasdaq listing, intended to broaden its investor base to AI-focused US capital, has created a new 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 advantage 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 concerns reported by Bloomberg suggest that the financing behind the AI investment cycle is itself 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 large cloud customers, the trajectory of Chinese domestic chip capacity, and whether SK Hynix and Samsung can offer forward guidance that rebuilds confidence in the sustainability of their earnings growth. For now, the market has delivered an unambiguous verdict: record profits, in this cycle, are not sufficient.