Williams now has a 12-1 record on clay this year after having beaten Samantha Stosur and Vera Zvonareva this week.
"I've played so many different players with so many different styles _ some play more clay-court tennis, others just hit the ball really hard," Williams said. "So just to come out on top so far is good, and I'm happy with my form and I'm going to try to keep that form tomorrow."
The fourth-seeded American will play either Lucie Safarova of the Czech Republic or Aravane Rezai of France.
Williams looked in control as she secured an early break to go up 3-1. The unseeded Peer responded immediately, earning three break points after firing a forehand pass down the line. Williams saved the first two before hitting a backhand into the net.
Williams eventually found some rhythm on serve, and closed out the first set having broken the Israeli again.
The American started to show her shot range as she led 3-0 in the second set with a deft drop-volley.
In the men's semi-finals, Rafael Nadal plays Nicolas Almagro and Roger Federer takes on David Ferrer.