In a microwave, melt butter and marshmallows; stir until smooth. Remove from the heat; stir in peanut butter until smooth. Gradually add cereal; toss to coat. Spread and press into a greased 13-in. x 9-in. pan; set aside.
In a microwave, melt chips; stir to coat. Spread over cereal mixture. Cover and freeze for 15-20 minutes or until chocolate is set.