In 3-quart saucepan, over low heat, melt chocolate and butterscotch morsels and peanut butter, stirring constantly, until well-blended. Remove from heat.
Add marshmallows and KELLOGG'S® RICE KRISPIES® cereal to chocolate mixture, stirring until well-coated. Press into 13 x 9 x 2-inch pan coated with cooking spray. Let stand in cool place until firm. Cut into 2 x 1-inch bars to serve.