Preheat oven to 350 degrees. Grease a 9'' x 9'' baking pan.
In a medium bowl, cream together peanut butter and butter or margarine. Gradually blend in white sugar, brown sugar eggs, and vanilla. Combine flour, baking powder, and salt and stir into the peanut butter mixture until well blended. Gently fold in chocolate chips.
Bake for about 25 minutes, check for doneness. You want a few crumbs on your test knife when you pull it out, it shouldn't be completely clean. Be careful not to overbake.