Concerns triggered by U.S. Treasury yields climbing to multi-decade highs weighed on South Korean equities today, as the market surrendered its opening gains. Heavy selling by foreign and institutional investors in the technology sector dragged the benchmark index lower, ending its two-day rally.

The Korea Composite Stock Price Index (KOSPI) opened 0.6% higher today (actually opening at 7,044.67 points), successfully reclaiming the 7,000-point mark. However, as foreign investors and institutions reversed course and turned to aggressive net selling midway through the session, the index fluctuated lower throughout the day, briefly falling below 7,000 points intraday, before ultimately closing down 0.89% at 6,941.39 points.

After-market data showed that foreign investors resumed selling today, with net sales of approximately 1.75 trillion Korean won, while institutions also net sold about 198 million Korean won. The market was left relying entirely on retail investors (net buying 740.56 billion Korean won) to prop it up.

As the two largest pillars by weighting in the KOSPI index, Samsung Electronics and SK Hynix mirrored the broader market's trajectory throughout the day, pressured by sector-wide profit-taking and macro headwinds from elevated U.S. Treasury yields. Both exhibited a weak pattern of "rallying early then pulling back, closing in the red for the day." Samsung Electronics closed down 1.45% at 272,000 Korean won. (It reached an intraday high of 279,000 Korean won alongside the broader market, and fell to a low of 270,000 Korean won.) With Samsung set to release its latest quarterly earnings report soon, market sentiment is increasingly cautious, and today's foreign investor reductions directly weighed on its share price.

SK Hynix closed down 3.37% (a sharp drop of 62,000 Korean won), with its final share price at 1,779,000 Korean won. As the leader in high-bandwidth memory (HBM), it bore heavier profit-taking pressure during today's session, with its decline significantly deeper than that of the broader market.