Shares of Japan's SoftBank Group plunged, following a broader slump in AI-related stocks as investors once again grew wary of the sector's lofty valuations.

The AI-led rally has pushed the S&P 500's forward P/E above 23—its highest since 2000, according to FactSet.

Shares of Japan's SoftBank Group plunged, following a broader slump in AI-related stocks as investors once again grew wary of the sector's lofty valuations.