Cornet entered the day 0-3 versus Williams but won four straight games in taking a lead of a set and a break and then held on for a 6-4, 6-4 victory. She'll face Venus Williams, against whom she is 0-3, in Saturday's finals.
Serena Williams had lost just two points through her first four games serving but Cornet broke for the first lead and then held for the first set. She added a break to open the second set but Williams was able to pull even.
Cornet went back ahead at 4-3 and Williams fought off four match points when serving before Cornet cashed in match point No. 5.
Venus Williams defeated No. 8-seeded Caroline Wozniacki 6-3, 6-2 in Friday's first semifinal. She amassed six breaks in nine games off Wozniacki's serve and lost just six points -- all in one game -- on serve in the second set.
Venus in recent years has been slowed by health issues, including Sjorgen's Syndrome which affects the autoimmune system, but played very well this week and hasn't dropped a set.
She'll be appearing in her second final this year. She lost in three sets to Ana Ivanovic in New Zealand in January. Her most recent WTA title came in October 2012 in Luxembourg. She's 44-28 all-time in title matches.
Cornet is 3-3 in WTA championship matches. She won last May at Strasbourg, France, in her most recent finals appearance.
The Dubai Duty Free champion will collect $471,841 and the runner-up will take home $251,648. Serena Williams and Wozniacki earned $135,064 as semifinalists.