In a large bowl melt together the marshmallows, chocolate chips, and peanut butter. Microwave at 50% power for 45 seconds at a time, stirring in between. Stir in chex cereal once melted.

Press into a 8x8 inch baking dish. Press well, so they stick together as a bar. Sift powdered sugar over the top.

Let cool completely before serving.

Store in the fridge for firm bars, room temperature for softer bars.