Alphabet, Google’s parent company, and several other Silicon Valley giants are having a rough week on Wall Street.

Shares of major tech companies have plunged in recent days as investors grow increasingly concerned about how much money they’re spending on AI and when and if those investments will pay off.

Alphabet, for example, had its worst day ever on the stock market Thursday, with shares plunging more than 12% and wiping roughly $500 billion off the company’s market capitalization.

The dramatic selloff came a day after Alphabet reported disappointing third-quarter earnings.…