In a large stock pot, melt the marshmallows over low heat. Stir in the chocolate chips and peanut butter until melted and well combined. Stir in the cereal to coat.
Press the cereal mixture into a greased 9x13 pan. Use a sheet of parchment or wax paper to really push the cereal down so that it holds it shape well. Sift powdered sugar on top of the bars. Let cool completely before cutting.
Store in the refrigerator for a firmer texture or at room temperature for a softer texture.