Following a massive rally driven by artificial intelligence, U.S. technology stocks finally show their first signs of fatigue.

Wall Street's current valuations rank among the highest in history, driven by AI hype, stretched metrics, and fragile market breadth dominated by mega-cap stocks.

The heaviest weight on the market was Nvidia, whose chips are powering much of the move into AI. It sank 3.5%.

The S&P 500 dipped 0.4% and was on track for a fifth straight modest loss since setting an all-time high last week. The Dow Jones Industrial Average was down 195 points, or 0.4%, as of noon Eastern ...