Line an 8x8 or 9x9 pan with aluminum foil so foil hangs over the edges so bars can easily be removed. Set aside.
Place butter in the microwave and heat for 1 minute, or until melted.
Stir in graham crackers, powdered sugar, and peanut butter and stir until well combined. Press mixture into the bottom of the pan.
Place chocolate chips in a microwave safe bowl and heat in the microwave for 45 seconds. Stir, then heat for another 30 seconds. Stir until smooth.
Pour chocolate over peanut butter bars and spread smoothly and evenly over top. Allow to cool for three hours then cut the bars while the chocolate is still soft. Cover and serve when the chocolate has hardened.