Line 13x9-inch pan with foil, with ends of foil extending over sides. Place grahams on bottom of pan, cutting as needed to completely cover bottom.
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 and mixture is well blended, stirring every 30 sec. Pour over grahams; spread to completely cover grahams.
Melt white chocolate as directed on package. Drop spoonfuls over semi-sweet chocolate; swirl gently with knife.
Refrigerate 1 hour or until firm. Use foil handles to lift dessert from pan; peel off foil. Cut dessert into bars.