Intel shares plunged in after-hours trading after its earnings report, as some forecasts said its fourth-quarter outlook would fall short of expectations.

Intel's third-quarter results released on Oct. 29 showed revenue of $16.51 billion, up 21 percent from $13.7 billion a year earlier. It was slightly above the $16.5 billion market estimate compiled by London Stock Exchange Group (LSEG). Adjusted earnings per share came to 52 cents, above the forecast of 40 cents.

Performance was mixed by segment. Data center and AI revenue jumped 78 percent to $7.3 billion. Client computing and physical AI revenue fell 5 percent to $8.1 billion, missing expectations. Global PC shipments in the second quarter fell 4 percent from a year earlier due to the impact of a sharp rise in parts prices including memory, Counterpoint Research said.

The fourth-quarter outlook also fell short of expectations. Intel forecast fourth-quarter revenue of $15.0 billion to $16.0 billion and adjusted EPS of 25 cents. Analysts forecast revenue of $17.1 billion and EPS of 43 cents.

Intel Chief Financial Officer David Zinsner said, "We see a PC market slowdown continuing at least through the first half of next year. Still, we remain optimistic about opportunities across the broader portfolio." He added, "We will continue to make measured investments in capacity and working capital to increase supply and support future growth."

Intel shares are up about 150 percent so far this year. But they have fallen about 23 percent in October amid concerns about the scale of investment in AI infrastructure.