In a large mixing bowl, combine graham cracker crumbs and powdered sugar until well blended. Pour in creamy peanut butter and melted unsalted butter. Mix until smooth and thick.

Line an 8x8 inch baking dish with parchment paper. Scoop the mixture into the dish and press it evenly, ensuring a smooth, packed surface.

In a microwave-safe bowl, add chocolate chips. Microwave in 30-second intervals until melted and smooth. Pour over the peanut butter mixture and spread evenly.

Chill the dish in the refrigerator for at least 1 hour, or until the chocolate is firm.

Once set, lift the bars from the dish using parchment paper and cut into squares. Serve chilled.