Place graham crackers in large resealable plastic bag; seal bag. Crush with rolling pin.

In large microwave safe bowl, microwave butter and peanut butter on high until almost smooth. Remove from heat and stir until completely melted. Add powdered sugar and graham cracker crumbs; blend well.

Spread mixture into 13×9 inch pan. In small microwave safe bowl, melt chocolate chips on high until almost melted; stir until completely smooth. Spread over mixture. Refrigerate just until chocolate is set. Cut into small squares. Store in refrigerator.