Williams needed just 65 minutes to deal with fourth seeded defending champion Agnieska Radwanska 6-0 6-3, while Sharapova, who won at Indian Wells earlier this month, demolished Serbia's Jelena Jankovic 6-2 6-1.
Sharapova extended her winning streak to 11 matches with a lopsided win in just over an hour against Jankovic, a former world number one struggling to regain her best.
The Russian's win was in stark contrast to her quarter-final victory over Sara Errani, where she made 57 unforced errors including 13 double-faults. She only double-faulted twice in this match.
''I just really thought I needed to step it up from my last match and play a little better,'' Sharapova said.
''I was really happy with the way I focused.''
Despite Sharapova's good form, Williams will start as clear favourite in Saturday's final - she is 11-2 in meetings with the Russian and has won the last 10 matches between the pair.
Williams, seeking a record sixth Miami title, is relishing the chance of taking on the woman directly below her in the world rankings.
"I love playing her. I love seeing her on the opposite side because she just brings out a good game. I just like the challenge of playing someone who has made history and who is doing so well," the American said.
"She's been playing awesome. I definitely expect a tough match."
One of just 10 women who have won all four Grand Slams, Sharapova has been collecting titles all over the world but has never won the Sony Open, played in her home state of Florida, despite playing four previous finals.
"It would mean so much to me," she said. "I love this city, it's the first city I landed in when I came to the United States as a little girl."
WTA Miami results
1-Serena Williams (U.S.) beat 4-Agnieszka Radwanska (Poland) 6-0 6-3
3-Maria Sharapova (Russia) beat 22-Jelena Jankovic (Serbia) 6-2 6-1
- Sports & Recreation
- Jelena Jankovic