NEW YORK >> U.S. stocks extended their selloff today as investors turned the page on a roller-coaster week with economic worries, the longest-ever federal government shutdown, and sky-high tech stock valuations dampening risk appetite.

All three major U.S. equity indexes were lower, with the tech-laden Nasdaq showing the steepest percentage loss.

The selloff punctuates a tumultuous week marked by mounting concerns over inflated valuations of artificial intelligence-related momentum stocks, which have provided much of the upside muscle to the stock market’s rally over recent months. All three indexes were on course to lose ground from last Friday’s close, with the Nasdaq headed for its largest weekly percentage drop since late March.

The information technology sector and broader semicond

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