The main bourse added 0.4 percent to finish at 6,641.02 points after climbing as high as 6,712.73, extending its winning streak to a seventh consecutive session.
Institutional investors purchased 351.1 billion Korean won (US$270 million) worth of shares, while foreign and retail investors sold 184.5 billion won and 130.3 billion won, respectively, indicating that the rally was increasingly driven by domestic institutional flows as other investors took profits.
The rally has been underpinned by sustained global inflows into artificial intelligence (AI)-linked semiconductor stocks, with the country's market capitalization surging more than 45 percent this year to around $4.04 trillion, overtaking the United Kingdom and highlighting its growing prominence in the global AI investment cycle. The gains reflect South Korea's outsized exposure to AI-linked sectors, amplifying its outperformance relative to regional peers.
Among major stocks, SK hynix rose 0.6 percent to 1,300,000 won, while Hyundai Motor jumped 5.9 percent to 555,000 won, reflecting a broadening of the AI-driven rally beyond semiconductors as investor interest extended to automakers amid growing expectations for partnerships in autonomous driving and robotics. Samsung Electronics, however, fell 1.1 percent to 222,000 won, signaling profit-taking in index heavyweights following recent gains.
In contrast, the junior KOSDAQ fell 0.9 percent to close at 1,215.6, reversing earlier strength as foreign and institutional investors offloaded a combined 786.8 billion won worth of shares. Retail investors bought a net 796.0 billion won, helping to limit losses. The divergence between the two major indexes highlights a shift toward large-cap, AI-linked stocks at the expense of higher-risk stocks.
Biotech and high-growth stocks led declines, reflecting continued pressure on high-valuation segments, even as some battery-related shares showed resilience.
The South Korean won edged down to 1,474.0 per dollar amid lingering global uncertainty.
Elsewhere in Asia, Japan's Nikkei 225 fell 1.1 percent to 59,917.5 after the Bank of Japan held its policy rate at 0.75 percent while signaling the possibility of further tightening. China's Shanghai Composite slipped 0.2 percent and Hong Kong's Hang Seng Index dropped 0.9 percent, as elevated energy prices and geopolitical risks weighed on regional sentiment.
Meanwhile, oil prices extended gains, with Brent crude hovering above $110 per barrel amid prolonged disruptions in the Strait of Hormuz.
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