Key Highlights

● KLA sank on October 22, ranking among the S&P 500's worst performers.

● KLA had no company-specific news, and its slide followed Lam Research's results and outlook.

● Lam guided December-quarter revenue to $8.6 billion, plus or minus $400 million.

● KLA makes inspection and measurement tools that chipmakers use to catch defects.

KLA Corp. (NASDAQ:KLAC) sank on Thursday, October 22, 2026, ranking among the worst performers in the S&P 500 after a supply warning from rival chip-equipment maker Lam Research (NASDAQ:LRCX) hit the whole group.

KLA had no company-specific news of its own. Its slide was a read-through from Lam's results and outlook, which sparked the Philadelphia Semiconductor Index's biggest one-day drop since June 23.

Lam's warning set the tone

Lam Research reported record quarterly revenue of $8.22 billion after the close on Wednesday but guided December-quarter revenue to $8.6 billion, plus or minus $400 million, with a midpoint slightly below what many investors had hoped for. More worryingly for the sector, Lam said supply constraints would limit growth.

Lam's chief executive said cleanroom and component constraints will "limit chip makers and equipment companies' ability to fully meet end demand" into 2027. Lam's chief financial officer said "things are going to continue to be constrained."

Because the problem was framed as an industry-wide issue affecting equipment companies, investors quickly applied it to Lam's peers. Lam itself tumbled, and Applied Materials (NASDAQ:AMAT) fell to close at $375.58. Dutch lithography leader ASML (NASDAQ:ASML) closed at $1,560.54.

What KLA does

KLA specializes in process-control and yield-management equipment, the inspection and measurement tools that chipmakers use to spot defects and keep production on track. Its systems are used at nearly every stage of chip manufacturing, which ties its fortunes closely to how much chipmakers spend on new factories and equipment.

That makes the company sensitive to the same capital-spending cycle as Lam and Applied Materials. If supply bottlenecks slow the pace at which new fabs can be built or equipped, the whole tool sector can feel the effect.

A broad AI and chip selloff

The pressure on equipment stocks was part of a much bigger selloff in artificial-intelligence and semiconductor names. The report from Meta Platforms (NASDAQ:META) showed heavy AI spending and negative free cash flow, while Nvidia (NASDAQ:NVDA)'s chief executive said: "The demand of the capital is much greater than the availability of the capital."

Nvidia closed at $212.21 and was one of the biggest drags on the S&P 500, according to market reports. Intel (NASDAQ:INTC), AMD (NASDAQ:AMD), SanDisk (NASDAQ:SNDK) and Marvell (NASDAQ:MRVL) all fell sharply, and test-equipment maker Teradyne (NASDAQ:TER) plunged.

The S&P 500 fell 93.74 points to 7,663.43, its worst session since July, and the Nasdaq Composite tumbled 694 points to 26,008.86, its steepest drop since June 5. The Nasdaq lost about $1 trillion in market value.

Outside technology, buyers were active: about two of every three S&P 500 stocks rose, according to market reports, as money rotated into consumer staples, health care, utilities and homebuilders.

Despite the losses, the Philadelphia Semiconductor Index remains sharply higher for the year, and it closed just above its 200-day moving average, a level that technical analysts often watch for signs of support.

KLA Listens for Its Own Supply Signals

KLA investors will be listening closely when the company reports its own results for any comment on supply constraints and customer spending. Before then, Teradyne reports on October 27 and Intel on October 29. Capital spending plans from Microsoft (NASDAQ:MSFT), Alphabet (NASDAQ:GOOGL) and Amazon (NASDAQ:AMZN) next week will also be closely followed, since they shape demand for the chips, and the chipmaking tools, that KLA's customers produce.