LINE 13x9-inch pan with foil, with ends of foil extending over sides of pan. Arrange grahams on bottom of pan, cutting as needed to completely cover bottom of pan; set aside.

MICROWAVE semi-sweet chocolate and peanut butter in medium microwaveable bowl on HIGH 1-1/2 to 2 min. or until chocolate is completely melted when stirred, stirring every 30 sec. Stir until well blended. Pour over grahams; spread with spatula to cover completely.

REPEAT microwave melting steps with the white chocolate. Drop spoonfuls of the white chocolate over chocolate-covered grahams. Immediately cut through the chocolate mixtures with knife several times for tiger-stripe effect.

REFRIGERATE at least 1 hour or until firm. Use foil handles to remove dessert from pan. Peel off foil. Cut dessert into bars. Store in tightly covered container in refrigerator.