South Korea's Stock Market Posts Its Biggest Single-Day Gain Ever on AI Rebound

A Historic Reversal on Wall Street's Coattails

In one of the most dramatic single-day reversals in global market history, South Korea's Kospi index surged nearly 18% on Friday, July 31 — its largest one-day gain on record. The Kospi rocketed up 17.9% to close at 6,695.45, marking its largest single-day gain ever. To put that in perspective, the benchmark's previous largest single-day gain, of nearly 12%, was back in October 2008 during the global financial crisis. Friday's move didn't just break that record — it shattered it.

South Korea's stock market staged its sharpest reversal on record, capping a month of wild swings that underscored how tightly the country's equity market has become tied to the global artificial intelligence trade. The catalyst was unmistakable: the rebound followed a powerful overnight rally in U.S. technology stocks after upbeat earnings from Microsoft, Amazon, and Meta reinforced expectations that spending on artificial intelligence infrastructure remains robust.

Samsung and SK Hynix Lead the Charge

Shares of South Korean technology giant Samsung Electronics surged 28%, while memory chipmaker SK Hynix soared 30%. These two companies are the twin engines of South Korea's tech economy, and their combined weight made Friday's rally feel almost seismic on the trading floor. Additional support came after SK Group Chairman Chey Tae-won disclosed purchases of SK Hynix shares, bolstering confidence in the world's second-largest memory chipmaker.

The benchmark Kospi index surged over 17% intraday, triggering the Korea Exchange's 'Sidecar' mechanism, which suspended program trading for 5 minutes — a circuit breaker designed to prevent runaway momentum. Foreign investors appeared to be the main force behind Friday's rally, while short-covering and mechanical rebalancing by leveraged exchange-traded funds amplified the gains. In other words, the bounce fed on itself, with multiple layers of buying pressure stacking up simultaneously.

The Brutal Week That Came Before

Friday's euphoria only makes sense against the backdrop of the carnage that preceded it. The Kospi had shed more than 17% in the previous three days as investors dumped technology stocks in part over worries about an AI bubble and rising competition from chipmaking and AI rivals in China. Reports that Chinese companies were developing domestic chip-manufacturing equipment had rattled investors who feared South Korea's semiconductor dominance could be eroded.

South Korea's Kospi posted its worst monthly decline on record, with a loss of over 33% in July surpassing the market's previous worst crashes in 1997 and 2008. That context makes Friday's rebound feel less like a resolution and more like a single dramatic chapter in a much longer story. Despite its big jump on July 31, the Kospi remains well below the peak of over 9,000 that it hit in June.

What This Means for Global Markets

The ripple effects spread across Asia. Japan's Nikkei 225 advanced 5.5% to reach 65,282.21, with SoftBank Group climbing 15% and semiconductor equipment manufacturer Tokyo Electron up nearly 11%. Taiwan's Taiex posted a gain of more than 7%. Back in the U.S., Wall Street's benchmark S&P 500 gained 1.7% on Thursday, the Dow Jones Industrial Average added 1.2%, and the technology-heavy Nasdaq composite rose 2.8%.

"The Korean stock market has been trading as if it has bipolar disorder, swinging from panic to euphoria almost overnight," said Jung In Yun of Fibonacci Asset Management. That assessment captures something important: the AI investment cycle has made markets extraordinarily sensitive to earnings signals. When a single quarter from Microsoft or Amazon can swing an entire national index by double digits, the interconnectedness of global tech finance has reached a new level of intensity. Future market stability remains contingent on global tech giants' capital expenditure guidance and sustained memory price momentum — meaning investors around the world will be watching every earnings call with fresh urgency.