The KOSPI jumped more than 5 percent and climbed back above the 9,000 level during the session, but it failed to hold the milestone. While a strong rebound emerged led by large-cap semiconductor shares, the Kosdaq fell more than 2 percent, underscoring a clear divergence between the two markets.

On June 25, the KOSPI ended up 459.28 points, or 5.42 percent, at 8,930.30. The index opened up 232.40 points, or 2.74 percent, at 8,703.42 and touched 9,000 during the session. It gave back part of its gains late in the day to close in the 8,900 range.

A buy-side circuit breaker was also triggered in the main KOSPI market amid the sharp rise. The Korea Exchange activated the measure at 9:07 a.m., halting the effectiveness of program buy orders for 5 minutes. This year, it was the 15th buy-side circuit breaker in the main market and the 28th combined for buy and sell-side measures.

In the main market, institutions led the gains, posting net purchases of 3.3469 trillion won. Retail investors and foreigners recorded net sales of 2.4964 trillion won and 816.8 billion won, respectively. Turnover totalled 50.3541 trillion won.

Among top market-cap stocks, strength in semiconductor shares stood out. SK Hynix closed up 337,000 won, or 13.06 percent, at 2,917,000 won. Samsung Electronics ended 18,000 won, or 5.29 percent, higher at 358,500 won.

Other semiconductor and information technology-related shares also rose, including SK Square, up 5.56 percent, and Samsung Electro-Mechanics, up 1.68 percent. Samsung C&T climbed 7.79 percent and Samsung Life Insurance rose 3.23 percent.

In contrast, Hyundai Motor fell 1.18 percent and LG Energy Solution dropped 3.69 percent.

The Kosdaq ended down 21.50 points, or 2.36 percent, at 887.81. It rose as high as the 930 level early, but extended losses over time and fell back below 900. With flows concentrating in KOSPI heavyweights, Kosdaq small and mid-caps were relatively sidelined, in what was described as a so-called "K-shaped" pattern.

The won-dollar exchange rate rose slightly. At the close, it stood at 1,544.40 won per dollar, up 0.90 won, or 0.06 percent, from the previous session.

The KOSPI rebound was attributed to bargain-hunting led by large-cap semiconductor shares after the sharp fall the previous day. Expectations for Micron results and forecasts of improving conditions in the memory sector stimulated semiconductor investor sentiment.