Preheat the oven to 350°F. Grease 9 x 13-inch pan with non-stick butter spray.
In a medium bowl, mix graham cracker crumbs, powdered sugar, and butter with a spoon.
Place the mixture in the bottom of the baking pan. Distribute the mixture evenly and press down and firmly with your fingers to "pack it" along the bottom and sides of the pan.
Place the pan in the oven and bake for approximately 5 to 8 minutes, until the sides begin to turn golden brown. Remove the pan from the oven and let it cool.
Lay the Hershey’s bars on top of the graham cracker mixture, covering all of the graham crackers as much as possible.
Place the pan back in the oven for approximately 3 minutes, until the chocolate just begins to melt and gets shiny.
Remove the pan from the oven and let it cool for 1 to 2 minutes. Place the marshmallows on top of the chocolate, packing them close to each other.
Turn your oven to broil, put the pan in the oven, and keep a close eye on your s’mores bars! The bars should broil for about 2 minutes, or until they begin to brown. Be careful not to overcook the bars.
Remove the pan from the oven and let the bars cool completely. Cut and serve.