By Rex Crum, MarketWatch

SAN FRANCISCO (MarketWatch) -- Advanced Micro Devices Inc. and SanDisk Corp. posted strong gains Friday as reaction to those companies' upbeat earnings reports led the day's activity in the tech sector.

AMD (AMD) shares climbed by 84 cents, or almost 13%, to $7.33 after the company said late Thursday that it had swung to a second-quarter profit of $61 million, or 8 cents a share, after reporting a loss in the same period a year ago. Excluding one-time items, AMD earned 9 cents a share to top the estimates of analysts surveyed by FactSet Research.

SanDisk (SNDK) was also on the rise, climbing $3.65 a share, or almost 9%, to $45.24. The flash-memory technology developer said late Thursday that it earned $248 million, or $1.02 a share, on $1.37 billion in sales, compared to a profit of $258 million, or $1.08 a share, on revenue of $1.18 billion in the same period a year ago.

Excluding one-time items, SanDisk would have earned $278 million, or $1.14 a share, while analysts surveyed by FactSet Research had forecast SanDisk to earn 99 cents a share on revenue of $1.34 billion.

Hard disk-drive maker Western Digital Corp. (WDC) rose by $2.47 a share, or more than 7%, to $37.31 after the company reported better-than-expected fourth-quarter results late Thursday.

Skyworks Solutions Inc. (SWKS) also had a good day, with its shares rising $3.24, or more than 14%, to $25.95. The company, which makes chips for use in smartphones and wireless devices, gave a better-than-expected third-quarter report and forecast fourth-quarter earnings that exceeded Wall Street analysts's estimates.

Microsoft Corp. (MSFT) shares were off by 6 cents at $27.03 on tepid reaction to the software giant reporting a 30% rise in its fiscal fourth-quarter earnings late Thursday.

The Nasdaq Composite Index (RIXF) shed 2 points to slip to 2,832, while the Philadelphia Semiconductor Index (SOX) and the Morgan Stanley High Tech 35 Index (MSH) edged into positive territory.