# South Korea's Kospi posts its biggest single-day gain ever after Microsoft earnings calm AI-bubble panic > Source: > Published: 2026-07-31 08:34:25+00:00 *South Korea's benchmark index surged 17.9% on July 31, 2026, its largest one-day advance in history, as Microsoft's blowout quarterly results flipped the switch on a week of brutal AI-driven selling.* Three days. That's how long it took for the Kospi to shed more than 17% and trigger back-to-back circuit breakers for the first time in the exchange's history. Then, in a single session, all of it was gone. The index closed at 6,695.45, reclaiming the 6,500-point level and logging a 17.9% gain that exceeded even its previous record jump of nearly 12%, set during the 2008 global financial crisis. Markets are not always slow to panic, and they're not always slow to forgive. The panic, this time, was about two overlapping fears: an AI bubble that might be inflating faster than the profits to justify it, and a China competitive threat that looked suddenly more real. According to Korea JoongAng Daily, the initial crash earlier in the week was triggered in part by reports that a Shanghai-based company backed by the Chinese government had begun producing domestically developed deep ultraviolet lithography tools, a category that Dutch firm ASML has long controlled. For investors already skittish about AI valuations, that was enough to spark a full-scale exit from Samsung Electronics and SK Hynix, the two companies whose revenue is most directly tied to the AI memory cycle. Microsoft reported Q4 FY2026 results on July 29, and the market's reaction on July 30 was immediate. The stock jumped roughly 15.5%, its best single day in nearly 18 years, after posting revenue of $90.01 billion and earnings per share of $4.74, both ahead of expectations. Azure revenue rose 43% year-over-year, beating the 40% consensus estimate. Paid Copilot seats passed 30 million, with net additions more than doubling sequentially. As Yahoo Finance noted, the Azure acceleration was the number that really mattered: it meant the hundreds of billions being spent on AI infrastructure was beginning to show up as real customer demand, not just on balance sheets. That's the read investors had been waiting for. Microsoft's capital expenditures hit $41 billion for the quarter alone, a 70% increase year-over-year, and FY2027 guidance puts capex at $255 billion to $260 billion. Under ordinary circumstances, that level of spending would alarm. Instead, because Azure's growth validated the investment, global markets took it as the clearest signal yet that AI monetization isn't a mirage. Seoul's rebound the following day was the direct consequence. Samsung Electronics surged 28%. SK Hynix hit its 30% daily price limit. Those moves weren't just relief from oversold levels. They reflected something more specific: both companies reported their own extraordinary results just the day before. Samsung's Device Solutions division posted a more than 250-fold increase in chip operating profit in Q2 2026, driven by AI data centers racing to secure high-bandwidth memory the company could barely produce fast enough, according to The National. SK Hynix, for its part, reported operating profit up 557% to a record 60.5 trillion won, with its entire 2026 production capacity already sold out to clients including Nvidia and Google, as Cryptopolitan reported. The selloff earlier in the week had been pricing in the end of that run. The rally on Friday was pricing in its continuation. ## Is this a turn or a bounce? Frankly, the speed of the reversal tells you as much as the reversal itself. When a market falls 17% in three days on fears about a Chinese lithography tool and vague AI-bubble anxiety, and then recovers the entire drop in one session after a single company's earnings beat, you're not watching a market that has done a lot of careful analysis. You're watching a market that was looking for a reason to sell and then found a reason to buy, in quick succession. That doesn't make the recovery meaningless. Microsoft's Azure number is real. Samsung's 250-fold chip profit surge is real. SK Hynix's record revenue and maxed-out production capacity are real. The AI memory demand cycle is not invented. But the Korean market's extraordinary sensitivity to a single American company's quarterly results illustrates something worth keeping in mind: the Kospi, and particularly its semiconductor heavyweights, has become a live proxy for global AI sentiment in a way that few other markets match. When that sentiment turns, the drawdowns are not gradual. The China threat isn't resolved either. Whether a domestically produced DUV lithography tool is a near-term competitive shift or a years-away capability is a legitimate open question, one that the market appeared to answer in opposite directions on consecutive weeks. What Seoul's record session confirms is that AI capex, for now, is still growing fast enough to absorb more competitors. What it doesn't confirm is that the next sharp correction won't arrive just as quickly as this one did. **Also read:** [Kioxia's 31-fold profit surge still wasn't enough to satisfy Wall Street](https://startupfortune.com/kioxias-31-fold-profit-surge-still-wasnt-enough-to-satisfy-wall-street/) • [China's homegrown DUV lithography machine goes into production and ASML loses 8% in a day](https://startupfortune.com/chinas-homegrown-duv-lithography-machine-goes-into-production-and-asml-loses-8-in-a-day/) • [Prop Firms Are Learning That No Single Funding Model Fits Every Trader](https://startupfortune.com/prop-firms-are-learning-that-no-single-funding-model-fits-every-trader/)