Williams, No. 1 in the world, had a masterful outing with her serve in a 6-3, 6-3 win over ninth-seeded Dominika Cibulkova. Williams had 12 aces and dropped only six points over nine games serving. She faced just one break point.
Cibulkova won a respectable 62 percent of the points on serve but Williams finished off three of her four break chances.
Sharapova, the No. 3 seed in Brisbane and fourth in the world rankings, defeated Kaia Kanepi 4-6, 6-3, 6-2. Sharapova was down a set and a break but didn't lose her serve after the first game of the second set.
Friday's semifinal will mark the 17th career meeting between Williams and Sharapova with Williams enjoying a lopsided 14-2 series lead. Williams has won the last 13 times she's played Sharapova, including going 4-0 against her in 2013. Sharapova hasn't beaten Williams since the 2004 Tour Championships.
The other semifinal will send No. 2-ranked Victoria Azarenka against fourth-seeded Jelena Jankovic. Azarenka survived a 2-hour, 15-minute challenge from Stefanie Voegele, eventually winning 6-4, 6-7 (7-9), 6-1. Jankovic topped No. 5-seeded Angelique Kerber 6-7 (8-10), 6-3, 6-1. Their match lasted 2 hours, 20 minutes.
Azarenka has a 5-4 series edge over Jankovic but Jankovic won their last meeting, a straight-set affair at the 2013 WTA Championships.