Start by spraying a 9x12-inch baking pan with non-stick cooking spray; set aside.
In a medium mixing bowl, combine the graham cracker crumbs, melted butter, peanut butter, and powdered sugar, mixing until smooth.
Spread the mixture evenly into the prepared 9x13-inch pan.
In a microwave safe bowl, melt the chocolate chips and 1/4 cup of peanut butter in the microwave in 15 second intervals, stirring well between each cooking interval until completely melted and smooth.
Spread the chocolate-peanut butter evenly over the peanut butter bars. Sprinkle the top of the bars with Reese's Pieces.
Chill the bars in the refrigerator for 30 minutes to set, then cut into 12 squares. Serve the bars cold or at room temperature.