Crush graham crackers, add sugar and melted butter.
Press into a parchment lined 9x13 pan.
Prepare brownie mix and poor over crust.
Bake at 350° for 22-25 minutes or until center is set.
Remove from oven and top with marshmallows and choc. chips immediately.
Turn oven to broil and put brownies under broiler for about 3 minutes or until just starting to brown.
Cool and cut into squares.