A buy-side sidecar was triggered on the KOSDAQ at 10:41 a.m. amid an aggressive rally in mid- and small-cap shares.
The KOSPI jumped 3.1 percent to close at 5,677.3 points, marking a fresh all-time high after hitting an intraday peak of 5,681.7. The strong upward momentum was broad-based across large-cap stocks, with the KOSPI 200 climbing 3.2 percent to 840.2.
The rally was symbolically anchored by Samsung Electronics, which settled at 190,000 won, up 5.9 percent, marking the first-ever close above the 190,000 level. The stock briefly touched 190,900 won within the market, setting a new record high. Gains followed overnight strength in U.S. technology shares, with continued enthusiasm surrounding artificial intelligence and semiconductor demand.
SK hynix added 1.6 percent to 894,000 won, while semiconductor equipment makers in the KOSDAQ market posted double-digit gains, reflecting renewed expectations for memory supply tightness and high-bandwidth memory pricing momentum.
The KOSDAQ soared 4.9 percent to 1,160.7, significantly outperforming the main board. A buy-side sidecar was triggered at 10:40 a.m., signaling an exceptional surge in futures-linked buying. The measure marked heightened volatility on the upside, underscoring strong speculative momentum in growth stocks.
Institutional investors led buying on the KOSPI with purchases of 1.64 trillion won, while foreigners were modest sellers of 923.2 billion won. Retail investors offloaded 860.5 billion won, reflecting profit-taking at elevated levels. On the KOSDAQ, both foreign and institutional investors turned strong buyers.
Beyond semiconductors, policy-driven themes gained traction. Shares of Hanwha Solutions surged 27.5 percent to 58,500 won, while Samsung SDI advanced 9 percent to 408,000 won, leading gains in the energy equipment and services sector, which rose more than 16 percent.
Investor attention also shifted to shipbuilding stocks after the U.S. administration unveiled its "America's Maritime Action Plan," which calls for cooperation with allied shipyards, including those in South Korea, under a so-called bridge strategy.
Under the proposal, initial vessel construction would take place in allied countries before production gradually transitions to U.S. facilities. The framework is seen as opening potential early-stage contract opportunities for Korean shipbuilders, given their established infrastructure and technical competitiveness.
However, uncertainties remain over how existing regulatory frameworks, such as the Jones Act, would be addressed or circumvented. Despite these unresolved questions, market participants broadly viewed the announcement as structurally supportive for Korea's globally competitive shipbuilding sector.
Korean won strengthened to 1,447.3 per dollar, down 5.7 won from the previous session, easing pressure on foreign flows. Precious metals advanced, with gold rising 2.1 percent to $5,009.5 per troy ounce and silver climbing 5.5 percent to $77.6.
Across Asia, Japan's Nikkei 225 rose 0.6 percent to 57,467.8, while China's Shanghai Composite fell 1.3 percent to 4,082.1.
Wednesday's session underscored a powerful convergence of semiconductor momentum, policy-driven industrial optimism and liquidity-driven small-cap strength, with Samsung's 190,000-won milestone serving as the defining symbol of the rally.
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