Philadelphia Semiconductor Index Closes Up 2.8%
The Philadelphia Semiconductor Index closed up 2.78% on Wall Street, rising for a second consecutive session. The three major U.S. stock indexes ended mixed on October 18 (local time), while AI and semiconductor stocks showed strength. The Dow Jones Industrial Average fell 0.18%, but the S&P 500 and Nasdaq Composite rose 0.17% and 0.39%, respectively. Oil prices fell for a third day, easing inflation concerns somewhat, but U.S. Treasury yields, which had dropped to the 4% range the previous day, climbed back above 5%, weighing on the market. West Texas Intermediate (WTI) crude for October delivery finished at $100.30 per barrel, while Brent for November closed at $103.87. AI and semiconductor stocks including Nvidia (1.34%), Broadcom (2.97%), AMD (2.70%), and Micron (3.92%) continued to rally. Seo Sang-young, executive director at Mirae Asset Securities, explained: "The Nasdaq managed to turn positive as semiconductor stocks extended their gains late in the session and large-cap tech stocks also showed resilience."
According to the Korea Exchange and financial data provider Yonhap Infomax, the KOSPI closed at 6,894.23 on October 18, down 15.68 points (0.23%) from the previous week. The index had plunged more than 3% early in the week to the 6,600 range, but narrowed its losses through repeated fluctuations. The KOSPI 200 Volatility Index (VKOSPI), dubbed 'Korea's fear gauge,' finished at 43.56, down 5.88 points (2.72%) from the previous week.
The early-week decline was driven by international oil prices and interest rates. Houthi rebels in Yemen threatened oil shipments through the Red Sea, keeping oil prices elevated above the $100 level, while the yield on the 10-year U.S. Treasury bond topped 5% for the first time in 19 years. Adding to this, calls from global AI company executives to slow the pace of AI development pressured the domestic stock market, which has heavy semiconductor weighting.
The impact of the AI slowdown debate did not last long. Some questioned whether Dario Amodei, CEO of Anthropic, raised the issue of regulating development speed preemptively as a strategic move ahead of the company's IPO this year. With news of Saudi Arabia resuming oil supply, oil prices and Treasury yields fell, and major stock markets including Korea's showed a rebound in the latter half of the week.
In this context, the Korea Exchange launched its after-market session (4 p.m. to 8 p.m.) for the first time last week. The number of tradable stocks, previously limited to around 600 under regulations in the enforcement decree of the Capital Markets Act, was expanded to cover most listed stocks.
Investor trading data for the KOSPI market last week (October 14–18) showed foreigners and retail investors selling a net 8.7627 trillion won and 271.3 billion won, respectively. Institutions posted net buying of 879.9 billion won, while other corporations—recently emerging as a key buying force thanks to large-scale share buybacks by Samsung Electronics and SK Hynix—purchased a net 8.149 trillion won. Foreign investors' top weekly net buys included Gaon Cable (119.8 billion won), SK Square (65.6 billion won), GS (57 billion won), LG Innotek (50.4 billion won), and LIG Nex1 (38.9 billion won). Top net sells were SK Hynix (3.4372 trillion won), Samsung Electronics (2.6341 trillion won), Samsung Electronics preferred shares (554.6 billion won), Netmarble (373.8 billion won), and Doosan (232.4 billion won).
Korean market sentiment indicators were mixed. The MSCI Korea exchange-traded fund (ETF) fell 0.59%, while the emerging markets index ETF rose 0.18%. However, the KOSPI 200 night futures rose 0.22%.
