Kospi, Kosdaq Halt Trading Twice in a Row — A First for Korea

South Korea's stock exchange halted trading marketwide for the second straight day on Wednesday, July 29, after both the Kospi and Kosdaq plunged more than 8% intraday — the first time in the country's history that circuit breakers have fired on back-to-back sessions.

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What Happened

The Korea Exchange activated a Kosdaq circuit breaker at 12:19 p.m. local time, followed by a Kospi-wide halt at 12:32 p.m., each freezing trading for 20 minutes after the respective index fell more than 8% from the previous close. It was the ninth marketwide circuit breaker in Korea this year and the country's 15th ever — meaning more than half of every circuit breaker triggered since the mechanism was introduced has now happened in 2026 alone. The move came a day after the Kospi already tripped a Level 1 breaker on Tuesday, sinking 8.02% to 6,213.51, so Wednesday's repeat marked an unprecedented two-in-a-row event.

Why It Matters — The Market Reaction

The damage concentrated in Korea's two chip giants. SK hynix dropped roughly 9.3% to 1,647,000 won and Samsung Electronics fell about 7.1% to 236,000 won, according to trading data reported the same day. Both stocks have now posted double-digit losses within the past week even after SK hynix reported a record quarterly profit, a mismatch I broke down in SK Hynix Posts Record Profit, Stock Sinks 8.76% on the Miss — the market cared more about guidance and AI-spending skepticism than the headline number.

The selloff wasn't isolated to Seoul. Wednesday's rout followed an overnight slide on Wall Street in which the Philadelphia Semiconductor Index fell more than 2% and Nvidia dropped nearly 5%, as investors grew more skeptical of the sustainability of hyperscalers' AI capital spending. That overnight weakness fed directly into Asian trading hours, hitting the two Korean chipmakers hardest since they are the most exposed to global memory-chip demand.

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Who and What Is Affected

Foreign investors were heavy net sellers of Samsung Electronics and SK hynix shares during the rout, amplifying the global semiconductor pullback already underway. Renewed fears about oversupply and weaker memory pricing — stoked in part by Chinese memory maker CXMT's expansion, a theme I covered in Samsung, SK Hynix Slide Again as CXMT's IPO Shaves a Year Off the Gap — compounded the pressure on both stocks.

For U.S. investors, the read-through runs straight through the memory and AI-hardware supply chain: Micron, AMD, and Nvidia all trade on sentiment tightly correlated with Samsung and SK hynix, since the three companies compete or partner across DRAM, HBM, and AI accelerator production. A Kospi selloff of this size has repeatedly spilled into U.S. premarket trading in chip names over the past several weeks. The broader Kospi itself is a useful gauge here: the index surged roughly 75% during 2025 on the AI and semiconductor boom, but has now slumped more than 30% since the start of July — a reversal of scale that puts the entire AI trade under scrutiny, not just one country's exchange.

What to Watch Next

• Regulatory response: Seoul's financial regulators had already moved to cap leverage after the initial chip crash, a step detailed in Seoul's Regulators Move to Cap Leverage After Chip Crash. A second consecutive circuit breaker raises the odds of additional intervention, including possible short-selling restrictions or further margin-related curbs.
• U.S. earnings and guidance: With SK hynix's results already having moved the tape once, upcoming commentary from Micron, AMD, and Nvidia on AI capex and memory pricing will be watched closely for confirmation or pushback on the oversupply narrative.
• Volatility persistence: Back-to-back circuit breakers are a signal of fragile market structure, not just a single bad news day. Whether Thursday brings a third straight halt — something that has never happened in Korea — will say a lot about whether this is a controlled correction or something more disorderly.
• Memory pricing data: Any fresh signal on DRAM or HBM contract pricing, especially tied to CXMT's ramp-up, will likely move both Korean chipmakers and their U.S. counterparts in tandem.

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

Two consecutive marketwide circuit breakers is a historic first for Korea, and it reflects a semiconductor sector-wide reckoning that isn't confined to one exchange. Whether this is a sharp but temporary flush of AI-trade excess or the start of a longer drawdown will likely come down to how Micron, AMD, and Nvidia frame their own AI spending and memory outlooks in the weeks ahead.