Kospi Soars 14%, Triggers Circuit Breaker on Chip Rebound

South Korea's Kospi ripped 12-14% higher at Thursday's open, tripping a dual buy-side sidecar with the Kosdaq for the first time in months, as Samsung Electronics and SK Hynix erased days of brutal losses in a single overnight reversal sparked by a Wall Street chip rally.

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What happened

At 9:06 a.m. local time, the Kospi jumped 693 points, or 12.40%, to 6,286.95, with the index later extending gains to roughly 13% and touching 6,320.82. The Kospi 200 futures index spiked 14.97% in a single minute, automatically triggering a buy-side sidecar that halts program buying for five minutes to cool volatility. The Kosdaq moved in lockstep, rising 6.2%-7.31% to the 685-692 range as its own futures gauge, the Kosdaq 150, surged 9.33%. Samsung Electronics opened up more than 20%, changing hands near 250,500 won, while SK Hynix jumped as much as 22-24% to around 1.6-2.1 million won. Samsung Electro-Mechanics and SK Square posted even larger swings. Foreign investors piled in with roughly 3.49 trillion won in net buying in the opening minutes.

Why it matters

The rebound followed one of the sharpest routs Korean chipmakers have seen this cycle. Just days earlier, on July 28, a semiconductor selloff had tripped a sell-side sidecar and then a full circuit breaker, sending the Kospi down 10.84% to 6,023.63 and the Kosdaq down 7.72%, with Samsung falling 13.39% and SK Hynix sinking 14.65% in a single session. From their 2026 peaks, Samsung had lost 44.7% (374,500 won to 207,000 won) and SK Hynix had lost 55.7% (2,987,000 won to 1,322,000 won), hit by a Q2 earnings miss and shareholder-return disappointment from SK Hynix, plus macro overhangs from U.S.-Iran tensions and a cautious Fed. Thursday's snapback reverses a meaningful chunk of that damage in a single session, underscoring just how tightly Korea's chip-heavy index is now wired to sentiment out of Wall Street's AI trade — the same dynamic I covered in Microsoft's $485 Billion Day Sparks a 2.8% Nasdaq Rally.

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Who and what is affected

The trigger came from overnight U.S. trading, where Microsoft's blowout fiscal Q4 earnings — $90 billion in revenue, up 18% year-over-year, with Azure growing 43% — added roughly $450 billion in market value and lifted the Nasdaq Composite 2.78% to 25,122.18. The rally spilled directly into memory chipmakers: the Philadelphia Semiconductor Index jumped 8.19%, Micron surged 18.36%, SanDisk soared roughly 25-26%, and AMD and Intel both posted double-digit gains. SK Hynix's U.S.-listed ADR moved in tandem, feeding straight into the Seoul open. On the ground in Korea, SK Group Chairman Chey Tae-won added to the rebound narrative by buying 3,620 more SK Hynix shares worth about 4.8 billion won — a follow-on to the purchase I detailed in Chey Tae-won Buys SK Hynix Stock for the First Time Ever — while Samsung has separately floated a special dividend and buyback-and-cancellation program to shore up investor confidence after the drawdown.

What to watch next

The bigger question is whether this is a durable turn or another whipsaw in a memory market that analysts still call a supercycle: Bank of America has framed 2026 as comparable to the 1990s DRAM boom, with UBS projecting industry revenue near $992 billion this year on AI data-center demand for HBM. But the sector's volatility has been unusually violent in both directions — a point worth remembering after I wrote about Micron's Down 31%. History Says the Drawdown Isn't Over Yet. Traders should watch whether Samsung and SK Hynix can hold today's gains into the close, whether foreign buying persists past the opening rush, and whether upcoming HBM order updates and the Fed's next signals reinforce or undercut the rebound.

This is not financial advice — always do your own research before making investment decisions.

Thursday's move is a reminder that in this cycle, a single earnings beat in Redmond can move markets in Seoul within hours — and that the same mechanism cuts just as hard on the way down as it does on the way up.