The Russian is in her third Roland Garros championship match having won the title in 2012 and holds a 3-0 winning record over Halep although the Romanian pushed her to three sets in the Madrid claycourt final earlier this year.
"It's very emotional to win and reach my first grand slam final," said Halep.
"Andrea's a great player but I think I was a little bit stronger. I tried my best and did everything I could to win the match."
She knows she will have to step up her performance against four-time major winner Sharapova who made the final for the third year in succession with a three-set win over Canada's Eugenie Bouchard 4-6 7-5 6-2 in a match full of beefy baseline shot-making.
It was the 19th time in a row that the never-say-die Sharapova had won a three-set match on clay, dating back to a loss against Justine Henin at Roland Garros in 2010.
For the fast-rising Bouchard, it represents the second time she has reached a grand slam semi-final, after this year's Australian Open, and the second time she has failed to go a step further, having lost to eventual champion Li Na in Melbourne.
"She played an unbelievable match. Her level was extremely high today and I am just fortunate to be the winner," Sharapova said.
"I would prefer to win in two sets, but she started so well. It was tough losing the first set, but that's not when the match is over."
AFP gjw
-AAP