Heat oven to 350°F. Place chicken breasts in ungreased 12x8-inch (2-quart) baking dish. Add mushrooms; sprinkle with Swiss cheese.
In small bowl, combine soup, sour cream and sherry; blend well. Pour over chicken.*
Bake at 350°F. for 50 minutes. Sprinkle with Parmesan cheese; bake an additional 5 to 10 minutes or until chicken is fork-tender and juices run clear. Place chicken on serving plate. Stir sauce if necessary to blend; serve with chicken.