Place 1/4 cup of butter in a microwavable bowl. Microwave for 30-second intervals until fully melted.
Stir in 6 cups of marshmallows, covering all marshmallows with butter. Microwave for 30-second intervals, stirring between each interval until marshmallows melt.
Fold in 6 cups of crispy rice cereal. Mix thoroughly. Press into a 9x9 inch greased pan.
In a microwavable-safe bowl, combine 1/2 cup of semi-sweet chocolate morsels and 1/2 cup butterscotch morsels. Microwave for 30-second intervals, stirring between each interval until the mixture completely melts.
Spread the mixture evenly over the rice crispy treats and allow to cool. To speed up the cooling process, place the treats in the refrigerator.