The Russian, seeded sixth after slipping to ninth in the world rankings, dominated the little Italian to win through in just under an hour.
"The further you go in the tournament, the harder it gets, and I really wanted to step up today and produce a good performance," Sharapova said.
"The first tournament on clay is always tough - it's important to improve with each match and I think I've done that this week.
"I know how good Sara is on the surface and I was extra ready to perform against her. She has a lot of experience and really knows how to play, so I had to take care of things on my side of the net."
Sharapova has endured something of a slump in recent months, going out of the Australian Open and Indian Wells in the early stages.
But following her quarter-final win over Agnieszka Radwanska, she seems to be back to her best and made light work of clay-court specialist Errani, seeded ninth.
WTA Stuttgart semi-final results
9-Ana Ivanovic (Serbia) beat 5-Jelena Jankovic (Serbia) 6-3 7-5
6-Maria Sharapova (Russia) beat 8-Sara Errani (Italy) 6-1 6-2
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