Bouchard, who is the No.5 seed at the International-level event, stormed out to a 63 30 lead and, after Mladenovic closed the gap to 63 32, reeled off another three games to seal the victory, 63 62.
"The surface is very fast and we were both hitting pretty hard," Mladenovic said. "But she was more solid - on the serve, on the return, in the rallies - she just played a really good match tonight."
"I'm very happy with the match tonight," Bouchard said. "I started well, breaking her early in the first set, and then I kept playing well from there, not losing serve until midway through the second set. But I just kept putting pressure on her and I'm happy I could close the match out in straight sets.
"She played well tonight too - I think it was a very high level of tennis out there."
The victory over Mladenovic not only puts Bouchard in the second WTA semifinal of her career - she was a semifinalist at Strasbourg earlier this year, losing a tight three-setter to Alizé Cornet - but the Canadian, currently ranked No.53, is now projected to break into the Top 50 for the first time.
Bouchard will have to beat another higher seed in the semifinals, with Lucie Safarova up next. The No.3-seeded Czech rallied from a break down in the second set to beat Lauren Davis earlier on, 62 64.
"It was a good match," Safarova said after the match. "I played very aggressively from the beginning and took the lead, and in the second set I just kept the pressure on her. I don't think she liked that. But it was nice to play out there with the great crowd - they've been great all week, and it's really nice."
Unlike Bouchard, Safarova is no stranger to finals - she has been to 11 of them before, and she's a former finalist here too, in 2009. "Genie is a great player - it's going to be tough, but I'm looking forward to it," Safarova said. "I played well today, so I hope I can keep my level up in the next one too."
Safarova and Bouchard will be playing against each other for the first time.
"It's going to be a tough match - she's very good and it's never easy playing a left-hander - but I hope I can keep playing like I did tonight," Bouchard said. "We'll see what happens tomorrow."