PLACE semi-sweet chocolate and white chocolate in separate medium microwaveable bowls. Microwave until completely melted, following directions on package. Add peanut butter to white chocolate; stir until well blended. Crumble half the cookies over chocolate in each bowl; mix well.
DROP spoonfuls of the chocolate mixtures onto wax paper-covered baking sheet, alternating the colours of the chocolates. Cut through chocolate mixtures several times with knife for marble effect.
REFRIGERATE at least 1 hour or until firm. Break into 14 pieces. Store in airtight container in refrigerator.