South Korea’s stock market was forced to stop trading on Tuesday, June 23, 2026, after the benchmark Kospi index collapsed in the opening hour, triggering an automatic safety halt run by the Korea Exchange. The index fell as much as 9% from last week’s record high before the exchange suspended trading for 20 minutes — one of only a handful of times in its history that the so-called circuit breaker has been pulled.
The plunge was led by the two companies that have powered Korea’s market all year: Samsung Electronics and SK Hynix, the world’s biggest makers of memory chips. At the worst point of the session, SK Hynix dropped more than 12% and Samsung lost more than 10%. By the time the market steadied, the Kospi had pared its loss to roughly 5% to 6%, sitting near 8,620.
The simplest explanation is that the rally had run extraordinarily hot. The Kospi is up about 78% so far in 2026 after climbing 76% in 2025, making it one of the best-performing major markets in the world. Much of that gain came from a global rush into chips used to build artificial intelligence systems. When a market climbs that fast, even a small scare can send investors racing to lock in profits — and that is what happened Tuesday.
Two pieces of news lit the fuse. The first was a report that South Korea will not be upgraded to “developed market” status in the next index review by MSCI, the firm whose stock benchmarks steer trillions of dollars in global investment. Many in Seoul had hoped an upgrade would pull in a fresh wave of foreign money. Word that it would not come this round took away a reason some overseas funds had to keep buying.
The second was a Korean media report that SK Hynix plans to slow production of high-bandwidth memory, or HBM — the specialized chips that feed AI servers — in order to make more of a different, higher-margin product. That rattled traders, because HBM is the exact business that turned SK Hynix into a star.
The timing was striking. Just one day earlier, on Monday, SK Hynix passed Samsung Electronics to become South Korea’s most valuable listed company — the first time any firm has held that title above Samsung since 2000. SK Hynix shares have soared more than 340% this year. The company is now the leading supplier of HBM chips to AI customers including Nvidia and Alphabet, and analysts estimate it controlled about 61% of the global HBM market last year, compared with 17% for Samsung.
The selling spread well beyond the chipmakers. Among the day’s hardest-hit names, DLG Exhibitions & Events fell 17.2%, Dae Won Chem dropped 15.9%, Enex lost 15.6%, Haesung DS shed 15%, and Hansol Technics slid 12.9%. The wide damage showed this was not just a chip story — it was investors pulling money off the table across the board.
The Korea Exchange uses the circuit breaker to cool panic. When the Kospi falls 8% or more and holds there for at least a minute, all trading stops for 20 minutes before it resumes. Earlier in the session the exchange also set off a “sidecar,” a separate curb that briefly freezes computer-driven sell orders. Both tools are designed to give human traders a moment to catch their breath.
For ordinary Koreans, the stakes are real. Everyday investors poured into the market during this year’s run, and the country’s national pension fund holds large stakes in both Samsung and SK Hynix. A sharp drop hits household savings directly. It also reaches far beyond Korea: Samsung and SK Hynix make a huge share of the memory chips inside phones, laptops, cars, and the data centers running AI, so swings in their shares ripple through the entire technology supply chain.
Whether Tuesday marks a brief stumble or the start of a deeper cooldown will depend on whether the AI buying spree holds up. The companies at the center of the sell-off are still reporting record demand for their chips. But the day was a sharp reminder that a market built so heavily on two names can fall just as fast as it climbed.
JBizNews Desk
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