Place cubed cream cheese in large mixing bowl and microwave for about 30 seconds, just until soft.
Add diced onion, cheese, and mayo to mixing bowl with cream cheese. Stir to combime.
Spoon into greased 1.5 baking dish (8x8). Bake at 375° for 25-30 minutes, or until bubbly and lightly browned on top. Serve with chips or crackers, enjoy.