Despite AI (artificial intelligence) momentum, semiconductor stocks faced another brake on their rise due to high oil prices and high interest rates during the second week of September (September 7–11). The strengthening won also shook export-heavy sectors such as cosmetics. In contrast, nuclear power stocks surged across the board amid expectations of U.S. investment.
According to Korea Exchange data on the 12th, KOSPI closed at 6,909.91 points during the second week of September, up 222.7 points (3.33%) from Jeonju. News of OpenAI's "GPT-6 Astra" launch at the start of the week stimulated investor sentiment for semiconductor stocks, and Samsung Electronics and SK Hynix surged. However, due to a potential military clash between the U.S. and Iran, international oil prices surpassed $100 per barrel on the 10th (local time), and the yield on 10-year U.S. Treasury bonds neared 5%.
As a result, Samsung Electronics rose only 1.57% for the week. During the same period, SK Hynix recorded a gain of 10.02%. Although it surged daily from September 7 to 9, rising by 12.69%, its gains were reduced after falling on the 10th and 11.
While semiconductor stocks stalled, nuclear power stocks led the market. Over the past week, the top gainer among KOSPI stocks (market capitalization of at least 1 trillion won and trading volume exceeding 100 billion won) was Korea Electric Power Corporation Technology, which surged 41.26%. Doosan (18.74%), Daewoo E&C (18.04%), Doosan Enerbility (14.65%), Korea Electric Power Corporation Industry (13.08%), and Hyundai E&C (12.70%) also ranked among the top gainers.
News that gas-fired power plants and nuclear power plant construction in the U.S. would be carried out through a $350 billion (approximately 469 trillion won) investment project stirred up nuclear power stocks. On September 7, the government reported to the ruling party about negotiations related to U.S. investment projects, and media outlets widely reported that the Ensynal Combined Cycle Power Plant construction project in Texas, U.S., was a strong candidate for the first U.S. investment project. Additionally, reports emerged that the final agreement would include plans to build eight nuclear power plants in the U.S., with a final signing (MOU) procedure possibly taking place as early as the 18th. Experts in the financial investment industry advised investors to pay attention to related beneficiary stocks, noting that domestic companies' opportunities to enter the U.S. market would increase through the U.S. investment project.
MLCC (multilayer ceramic capacitor) companies such as Samwha Condenser surged amid expectations of rising MLCC supply prices and potential shortages. Samwha Condenser rose 25.14% for the week. Gaon Cable jumped 19.81% for the week on news that it would supply medium-voltage cables to a Canadian power company.
In contrast, stocks that lost momentum saw significant declines as profit-taking orders emerged. The biggest loser over the week was NHN, which plummeted 21.12%. NC also fell by 7.43%. Oh Dong-hwan, a researcher at Samsung Securities, explained, "NHN's stock price dropped due to profit-taking after its short-term rise," and added, "NC saw selling pressure as momentum faded following the conclusion of the global gaming event 'Gamescom 2026' in Germany."
Some stocks were also hit by a decline in the won-dollar exchange rate. The won-dollar exchange rate has been fluctuating between 1,330 and 1,340 won. As the won strengthened, export-heavy sectors such as cosmetics slipped. Darby Global fell 12.07% for the week, marking the second-highest decline among KOSPI stocks. APR and Kolmar Korea declined by 5.58% and 3.09%, respectively. Although not part of the cosmetics sector, Samyang Foods, which has a high export ratio, also fell 9.81%.
With the U.S. Federal Open Market Committee (FOMC) scheduled to meet on the 15th–16 (local time), external variables are expected to continue influencing the stock market. Kang Jin-hyuk, a researcher at Shinhan Investment Corp., stated, "There is growing caution regarding macro events."
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