Stocks Close at Worst Levels Since July: S&P 500 Falls 1.11%, Nasdaq 1.88%, Chip Index 4.3%

Since this morning's September CPI report showed annual inflation at 3.7%, against 3.6% expected, U.S. stocks went from a midday slide to a hard close. The S&P 500 finished Wednesday, Oct. 14, down 1.11%. The Nasdaq Composite fell 1.88% to 26,692.87. Both posted their worst day since July.

The Dow Jones Industrial Average barely moved. It slipped 48.62 points, or about 0.1%, to 51,621.48. The S&P 500 has now lost ground on five of the six sessions since it set its all-time high.

Chips and AI infrastructure take the hit

The damage was concentrated in the companies building out AI data centers. A benchmark semiconductor index dropped 4.3% and is down roughly 12% over the past week.

Marvell fell 8.7%. Oracle sank 8.8%. Dell dropped 11.3%. Nvidia lost 3.2% and sits about 7.5% below the record high it hit earlier this month.

South Korea's KOSPI index has fallen 12% over five days, and the sell-off in memory and chip names carried into U.S. trading. Chinese chipmaker CXMT announced progress on advanced memory chips this week, which has stoked worries about competition for U.S. and South Korean manufacturers whose outlooks analysts describe as "priced to perfection."

Higher bond yields and sticky inflation are also raising borrowing costs for a data center buildout that leans heavily on debt. The risk falls hardest on the more leveraged corners of the AI ecosystem.

Not everyone is selling the story

The demand case for AI hardware took a hit in price but not in fundamentals. Chip equipment maker ASML posted record third-quarter sales today and raised its full-year outlook, citing strong AI demand.

Steve Sosnick, chief strategist at Interactive Brokers, told CNN the problem is expectations. "There's just so much good news priced into the chip sector right now that you're going to find it's susceptible to meandering without some fresh catalysts," he said. "Trees don't grow to the sky."

The next catalyst arrives Thursday, Oct. 15, when Taiwan Semiconductor reports earnings. Investors are looking to it for further confirmation of AI demand.

Banks, Apple and oil

Bank earnings added to the mix. Bank of America closed down 5% after a $1.2 billion regulatory penalty weighed on its results. BlackRock shares rose after third-quarter earnings beat analyst expectations. Banks reporting this week have indicated consumers are holding up despite higher interest rates.

Apple's market capitalization crossed $5 trillion again in intraday trading, months after it first touched that level in late July.

Brent crude futures stayed above $105 a barrel as Houthi attacks on Saudi Arabian energy facilities continued. Higher gas and energy prices drove the inflation reading, and the hotter print lowered the odds that the Fed will hold rates steady at its policy meeting this month.

Paper wealth takes a hit

Forbes' valuation tracking shows the world's richest people lost about $50 billion as stocks slid. Elon Musk remains the wealthiest person by a wide margin despite losing tens of billions of dollars over two days, Forbes said. Much of his net worth comes from his SpaceX and Tesla stakes, which can swing sharply with market moves.

Those are changes in estimated valuations, not realized losses.

The near-term test is Thursday's Taiwan Semiconductor report, followed by the Fed's meeting later this month, where traders are weighing whether a hike is back on the table.