Preheat the oven to 400 degrees F (200 degrees C). Line an 8x8-inch square pan with aluminum foil, leaving a 1-inch overhang on sides.

Crumble graham crackers in a bag; pour into a bowl. Stir in butter and brown sugar until well mixed. Press graham cracker mixture into bottom of prepared pan to form crust.

Bake in the preheated oven until crust is lightly browned and smells toasted, about 7 minutes.

Remove the pan from the oven; cover crust evenly with marshmallows. Sprinkle chocolate chips over marshmallows.

Bake in the preheated oven until chocolate chips are melted and marshmallows are browned, about 3 minutes.

Let s'mores rest in the pan until cool, about 30 minutes.