Key Highlights

● Micron slid to $934.27 on October 29 with no company-specific news.

● Alphabet's negative free Cash Flow of $9.07 billion revived AI cost worries.

● The PHLX Semiconductor index snapped a four-day winning streak.

● Amazon reaffirmed a $220 billion capex plan after Thursday's close.

Micron (NASDAQ:MU) had no news of its own on Thursday, but renewed doubts about the cost of the artificial intelligence buildout sent memory stocks sliding.

Memory loses its shine

Micron Technology has been one of the great beneficiaries of the AI boom. On Thursday, it became one of its casualties. The stock slid to close at $934.27 on October 29, according to market data, as memory stocks cooled amid worries about AI Capital spending, one report said.

No company-specific news was behind the drop. Micron, which makes the DRAM and NAND memory chips that store and move data in everything from smartphones to AI servers, simply got caught in a sharp shift in sentiment.

The PHLX Semiconductor Index snapped a four-day winning streak, and the Nasdaq-100 fell to 29,402.51.

The Alphabet trigger

The day's selloff in chips traced back to Alphabet (NASDAQ:GOOGL). Its results, released on Wednesday evening, included negative free cash flow of $9.07 billion and quarterly capital spending of $51.36 billion. The stock suffered its worst day since its 2004 IPO, erasing about $500 billion in market value.

Media reports said the results "reignited concerns over mounting AI costs." For memory makers, that worry hits close to home. AI servers require enormous amounts of high-bandwidth memory, and any hint that cloud giants might rethink their budgets can quickly ripple down the Supply chain.

One senior market analyst captured the shift in mood: "markets are no longer rewarding companies simply for investing heavily in AI."

A crowded exit from chips

Micron was not alone. Sandisk (NASDAQ:SNDK), another memory and storage name, fell during the regular session before reporting results after the bell that topped expectations and included an 8-for-1 stock split. Its after-hours reaction was mixed, according to various reports.

Across the sector, Marvell Technology (NASDAQ:MRVL) sank to $218.34 on reported Takeover talks with Lumentum (NASDAQ:LITE), AMD (NASDAQ:AMD) closed at $566.42 and Nvidia (NASDAQ:NVDA) edged lower to $213.66. Intel (NASDAQ:INTC) slipped in the regular session before plunging after hours on weak guidance. Overseas, Samsung fell after a profit miss in its chip division, according to market commentary.

KLA (NASDAQ:KLAC) was a standout exception, jumping on record quarterly revenue.

Money on the move

The broader market told a different story. More than 400 S&P 500 members rose even as the index slipped 23.59 points to 7,720.39. The Russell 2000 climbed 28.71 points to 2,859.22, and health care, real estate and utilities all rallied.

"There's plenty of other places to go with your money outside of the AI trade that have pretty decent prospects," one market strategist said.

That rotation is a challenge for high-flying chip stocks like Micron, whose share price reflects strong expectations for AI-driven memory demand. When investors look for safer ground, those expectations are the first to be questioned.

The rates angle

Economic data added another layer. Third-quarter GDP grew faster than forecast, with Business Investment surging, and September PCE Inflation ran hot. The Federal Reserve held rates steady on Wednesday, but two officials dissented in favor of a hike, and traders continued to lean toward a December increase. Higher rates tend to weigh on richly valued growth stocks.

What to watch

The next big signal for Micron comes from its customers. Amazon (NASDAQ:AMZN) reported after Thursday's close and reaffirmed a $220 billion capex plan, a sign that at least one cloud giant is not pulling back. How memory stocks react to that commitment on Friday will show whether the sector's selloff was a one-day wobble or the start of something deeper.

Arm (NASDAQ:ARM) reports in early November, offering another read on chip demand. Friday's Employment Cost Index and the Fed's December 8 to 9 meeting will also shape the backdrop for semiconductor stocks heading into year-end.