Line an 8x8 inch baking pan with parchment paper, leaving an overhang on the sides.
In a medium bowl, combine melted butter, graham cracker crumbs, granulated sugar, and 0.5 cup peanut butter. Mix until well combined and crumbly.
Press the mixture evenly into the prepared baking pan to form the base layer.
In a microwave-safe bowl, combine chocolate chips and 0.5 cup peanut butter. Microwave in 30-second intervals, stirring between each, until smooth and melted.
Pour the chocolate peanut butter mixture over the base layer and spread evenly.
Refrigerate for at least 2 hours, or until firm.
Lift the bars out of the pan using the parchment paper overhang. Cut into squares and serve.
Notes
These bars can be stored in an airtight container in the refrigerator for up to a week.