Tumbling microprocessor prices have prompted Advanced Micro Devices (AMD) to warn of a dip in earnings ahead of its fourth-quarter (Q4) results at the end of the month.

The chipmaker expects Q4 operating income to be positive but "substantially lower" than in the third quarter.

The company, which gave no Q4 figure, reported operating income of $119 million ($61m) in the third quarter.

AMD attributed the dip in earnings to a sharp drop in prices for PC processors, which was largely offset a "significant increase" in unit sales.

For the fourth quarter, which ended 31 December, AMD expects revenue, excluding its recent acquisition of ATI Technologies, to increase 3% from the $1.33 billion (£684bn) reported in the third quarter.

Analysts had been expecting AMD to report fourth-quarter revenue of $1.85 billion and earnings per share of $0.23, according to Thomson Financial.

AMD, which will report its fourth-quarter results 23 January, has been taking semiconductor market share away from rival Intel in the last year with new dual-core processors, forcing Intel into a defensive posture.