Russian second seed Sharapova, who was also a semi-finalist in 2007 and 2011, eased past Estonia's Kaia Kanepi 6-2, 6-3 while fourth-seeded Kvitova ended Kazakh qualifier Yaroslava Shvedova's dream run with a 3-6, 6-2, 6-4 win.
"I am happy to be back in the semi-finals. I love coming back here to challenge myself to go further in the tournament," said Sharapova, who can reclaim the world number one spot if she gets to Saturday's final.
"I won two tournaments coming into Paris in Stuttgart and Rome and they gave me a lot of confidence. But every event is different. I am just happy to improve and I know it'll get tougher from here."
Kanepi was broken seven times in the match and admitted that Sharapova had too much firepower for her.
"She attacked all the time, I didn't have any time to hit my shots and I just couldn't get any rhythm out there. I was also very nervous and I am just sorry I didn't get to spend more time on the court," she said.
"Maria is playing really well, she can win the tournament."
On another chilly, gloomy day in the French capital, Sharapova and Kanepi, who made the quarter-finals in 2008, exchanged breaks in the first two games before the Russian picked up two more in the third and seventh games.
Kanepi, the 23rd seed, saved two set points in the eighth game, but was powerless on the third when Sharapova unleashed a fierce serve down the middle which the Estonian could only deflect into the stands.
The start of the second set was just as untidy as the first with the world number two giving up a break to slip 2-0 down on a fourth double fault and then retrieving it immediately in the next to trail 2-1.
Kanepi, who put out former world number one Caroline Wozniacki in the third round, was quickly another break down while a Sharapova hold to love gave the Russian a 4-2 lead.
Sharapova squandered the opportunity to serve out the match in the eighth game when she was broken to love, but it was a brief respite for the 26-year-old Estonian who ballooned a forehand wide to hand Sharapova the tie in the next.
Kvitova reached her first French Open semi-final with a battling victory over world number 142 Shvedova who had knocked out defending champion Li Na in the fourth round.
Shvedova was bidding to become the first qualifier to make the last four at Roland Garros and she got off to a roaring start against Kvitova and was even 4-2 ahead in the deciding set before she wilted.
Kvitova held in the seventh game of the decider and immediately put pressure on Shvedova's serve to level the match at 4-4, followed by a crucial hold.
Serving at 4-5, nerves got the better of Shvedova, allowing the world number four to convert her second match point for a place in the semi-final.
"Every point that we played was really tough," Kvitova said.
"I knew that I had to change my game. It wasn't easy and I'm really happy that my serve helped me and I played my aggressive game again."
Kvitova's clash with Sharapova on Thursday will be the pair's third Grand Slam clash within a year.
The Czech triumphed in the Wimbledon final before Sharapova defeated the Czech in the Australian Open semi-finals.
Crucially, Sharapova enjoyed a straight sets victory in the semi-finals on clay in Stuttgart in the run-up to Paris.
Thursday's other semi-final sees Australia's Samantha Stosur taking on Sara Errani of Italy.
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