US stocks today: S&P 500, Nasdaq open higher as chip stocks gain; US-Iran tensions in focus

US markets opened mixed on Monday, with the S&P 500 up 0.12% at 7,491.6 and the Nasdaq Composite up 0.18% at 25,918.31, while the Dow Jones fell 98.9 points or 0.19% to 52,249.44. Chip stocks led the gains at the opening bell. Geopolitical risk from US-Iran tensions remained a key focus for investors.