Preheat oven to 350. In a large bowl, cream the butter, peanut butter, sugar and brown sugar. Add eggs, one at a time, beating well after each addition. Beat in vanilla. Combine the flour, baking powder and salt; gradually add to creamed mixture. Stir in chocolate chips.
Spread mixture into a greased 13x9 baking pan. Bake at 350 for 45-50 minutes or until a toothpick inserted near the center comes out clean. Cool on a wire rack. Cut into bars.