[Edaily Reporter Shin Ha-yeon ] The domestic stock market plummeted by more than 5% on the 5th amid massive sell-offs by foreign investors. Concerns over data center regulations came to the fore in the wake of the “Blue Tsunami”—the Democratic Party’s sweep of both the Senate and House of Representatives in the U.S. midterm elections—leading to concentrated selling, particularly in semiconductor and artificial intelligence (AI) infrastructure stocks. Sell-side circuit breakers were triggered simultaneously on both the KOSPI and KOSDAQ that day.

According to MP Doctor on the 5th, the KOSPI closed at 5,383.80, down 300.00 points (5.28%) from the previous trading day. This is the lowest closing level since April 3 (5,377.30). The index, which opened at 5,580.09, plummeted to as low as 5,336.88 during the session.

Along with the sharp drop in the index, the KOSPI’s market capitalization also fell from 4,690.4921 trillion won the previous day to 4,441.8334 trillion won on this day—a decrease of 248.6587 trillion won in just one day. Compared to the 4,969.4424 trillion won recorded on the 28th of last month, this means 527.6090 trillion won has evaporated in just six trading days.

On this day, foreign investors drove the index down by net selling 3.4248 trillion won worth of stocks on the KOSPI market alone. Retail investors and institutions made net purchases of 2.2769 trillion won and 841.7 billion won, respectively, but this was insufficient to defend the index. Program trading showed a net selling position of 1.9085 trillion won, driven primarily by non-arbitrage trades.

As the sell-off intensified, a sell-side sidecar was triggered on the stock market at 10:16 a.m. This occurred because the Mini KOSPI 200 futures had fallen 5.21% below the reference price for one minute. At that time, net selling via program trading totaled 660.8 billion won. This marks the 56th time a sidecar has been triggered on the KOSPI this year, and the 29th time a sell-side sidecar has been activated.

Large-cap semiconductor stocks saw particularly sharp declines. SamsungElectronics(005930)closed at 201,500 won, down 7.57%. This marks the first time in about three months—since July 29—that SamsungElectronics’ share price fell below 200,000 won during trading hours. SK hynix(000660)closed at 1,264,000 won, plunging 9.46%.

SKSQUARE(402340) SamsungElectroMechanics(009150)fell 10.01%, and dropped 15.34%. This reflects concerns—spilling over into the domestic AI infrastructure value chain—that licensing requirements and regulations on electricity and water supply in major U.S. data center regions could tighten following the Democratic Party’s landslide victory. In contrast, some large-cap non-AI stocks, such as (up 3.53%), (up 3.63%), and (up 1.67%), rose, demonstrating a clear divergence in market trends. HyundaiMotor(005380) KB Financial Group(105560) SAMSUNG BIOLOGICS(207940)

The KOSDAQ also closed at 678.41, down 36.54 points (5.11%) from the previous trading day. This is the lowest closing price since July 30 (644.78). During the session, the index fell as low as 673.38. Foreign and institutional investors recorded net sales of 76 billion won and 102.4 billion won, respectively, while retail investors made net purchases of 172.1 billion won.

On the KOSDAQ market, a sell-side circuit breaker was triggered at 2:27 p.m. This occurred after the KOSDAQ 150 futures fell 6.07% and the KOSDAQ 150 Index dropped 5.43% for one consecutive minute. This marks the 35th time a circuit breaker has been triggered on the KOSDAQ market this year, and the 16th time a sell-side circuit breaker has been activated.

Overnight on the New York Stock Exchange, the Dow Jones, S&P 500, and Nasdaq indices rose 3.03%, 1.58%, and 1.44%, respectively, while the Philadelphia Semiconductor Index fell 3.13%. While expectations of policy changes stemming from “Blue Tsunami” acted as a positive factor for U.S. hyperscalers, they created regulatory uncertainty for semiconductor and AI infrastructure companies—which are sensitive to data center investments—and this trend appears to have been amplified in the domestic stock market as well.