[Edaily Reporter KIM YOON-JEONG ] The KOSPI plunged nearly 6% on the 19th, erasing all of this month’s gains. This was due to SamsungElectronics and SK hynix plunging 7.82% and 9.75%, respectively, dragging down the index as investor sentiment froze amid a sharp rise in U.S. long-term Treasury yields and oil price volatility stemming from the Middle East. Shortly after the market opened, a sell-side circuit breaker was triggered on the stock market.

According to MP Doctor, the KOSPI index closed at 6,471.17 today, down 398.66 points (5.80%) from the previous trading day. The index opened at 6,528.77, down 341.06 points (4.96%) from the previous close, and fell as low as 6,400.81 during the session.
The KOSPI had been rebounding since the 10th of this month, rising to 6,869.83 on the 18th, but it plummeted 5.80% on this day alone, erasing all of its August gains. It fell to a level 124.28 points (1.88%) lower than the closing price on July 31, the end of last month (6,595.45).
By investor type, while retail investors engaged in large-scale bargain hunting, foreign and institutional investors both sold off their holdings, putting downward pressure on the index. In terms of supply and demand, based on NextTrade (NXT) data, retail investors made net purchases totaling 5.6403 trillion won on the stock market. In contrast, foreign and institutional investors made net sales of 4.0242 trillion won and 1.7926 trillion won, respectively.
Shortly after the market opened at 9:06 a.m., the KOSPI 200 futures price fell 6.02% from the reference price, triggering the sell-side circuit breaker on the stock market. As a result, the execution of program sell orders was temporarily suspended for five minutes.
Overnight, U.S. stock markets fell across the board as rising long-term Treasury yields coincided with oil price volatility stemming from the Middle East. The Nasdaq Composite Index fell 1.33%, and the S&P 500 Index dropped 0.69%. Investor sentiment toward risk assets weakened as international oil prices rose amid fading hopes for U.S.-Iran negotiations, and the yield on the 30-year U.S. Treasury note climbed to 5.33% during the session—its highest level since 2007.
In particular, profit-taking sold off heavily, particularly in artificial intelligence (AI) and semiconductor stocks, due to the burden of rising interest rates. The Philadelphia Semiconductor Index (SOX) plummeted 4.98%, with Micron (-7.06%), SanDisk (-8.89%), and Western Digital (-7.43%) all posting sharp declines. SK hynix American Depositary Receipts (ADRs) also plunged 9.20%.
Market analysts suggest that this rise in long-term interest rates stemmed from Treasury supply-and-demand dynamics and inflation concerns rather than a reassessment of the U.S. monetary policy path. They explain that as long-term yields rose more sharply than short-term yields—which are sensitive to policy rates—correction pressure intensified on AI and growth stocks, which are sensitive to the discount rate applied to future earnings.
Cho A-in, an analyst at SamsungSecurities, stated, “This correction is more a pullback following the recent short-term rally than a sign of deteriorating corporate fundamentals,” adding, “From the low at the end of July through yesterday, the KOSPI had risen by about 23% and the Philadelphia Semiconductor Index by about 21%.”
She continued, “Given that the semiconductor market remains robust and the correction has already progressed significantly following the period of volatility that began in June, we believe the potential for further declines is limited.” She added, “It would be appropriate to adopt a strategy of seeking investment opportunities, particularly in sectors with high earnings visibility, while monitoring whether the upward trend in interest rates subsides.”
Kim Seok-hwan, an analyst at MIRAE ASSET SECURITIES, also identified rising long-term interest rates as the key factor behind this correction. Analyst Kim analyzed, “This correction appears to reflect the relatively significant impact of rising long-term interest rates and changes in credit costs, rather than concerns about the growth potential of the AI industry itself.”
However, he drew a line regarding the possibility that rising long-term interest rates could lead to structural weakness in domestic semiconductor stocks. He elaborated, “There does not seem to be much need to overinterpret this as a structural concern regarding the AI or semiconductor sectors,” adding, “Especially given that the forward price-to-earnings (P/E) ratios of SamsungElectronics and SK hynix have fallen to around 3 to 4 times, the likelihood that valuation pressures resulting from rising long-term interest rates will manifest with the same intensity as they do for high-P/E growth stocks is limited.”
SamsungElectronics(005930), the company with the largest market capitalization on the KOSPI, closed at 247,500 won, down 21,000 won (7.82%) from the previous trading day. SK hynix(000660), the second-largest by market cap, closed at 1.5 million won, plummeting 162,000 won (9.75%).
Stocks related to these two blue-chip companies also fell sharply. SKSQUARE(402340)closed at 1,004,000 won, down 131,000 won (11.54%), while SamsungElectronics(005930) preferred stock fell 7.75% and SamsungElectroMechanics(009150)dropped 3.68%.
In addition, HyundaiMotor(005380)(-4.83%), KB Financial Group(105560)(-1.25%), and SAMSUNG C&T CORPORATION(028260)(-5.96%) all fell. On the other hand, LG Energy Solution(373220)(1.85%), SAMSUNG BIOLOGICS(207940)(0.85%), and HANWHA AEROSPACE(012450)(2.71%) closed higher.
The KOSDAQ market plummeted early in the session but recovered a significant portion of its losses. The KOSDAQ index closed at 824.46, down 9.74 points (1.17%) from the previous trading day. The index opened at 810.08, down 24.12 points (2.89%) from the previous close, and at one point rose as high as 840.50.
In the KOSDAQ market, foreign investors were net buyers of 46.3 billion won worth of stocks, while institutional investors were net buyers of 45.8 billion won worth. In contrast, retail investors were net sellers of 100.5 billion won worth of stocks.
Among the top market-cap stocks, Alteogen Inc.(196170)rose 1.85% to 303,500 won, and ECOPRO BM CO., LTD.(247540)also climbed 0.64% to 109,800 won. ECOPRO CO., LTD(086520)(-1.03%), Rainbow Robotics(277810)(-1.60%), JUSUNG ENGINEERING Co.,Ltd.(036930)(-4.29%), HLB INC.(028300)(-2.43%), and WONIK IPS Co.,Ltd.(240810)(-2.76%) all fell. LEENO Industrial Inc(058470)(0.15%), EO Technics Co., Ltd.(039030)(0.24%), and Peptron, Inc.(087010)(3.28%) closed higher.