Prepare the brownie mix according to package instructions. Bake as directed. Five minutes before brownies are finished baking, remove from the oven.
Top with the chocolate chips and marshmallows. Return to the oven to finish baking.
While the brownies are baking for the last five minutes, add the peanut butter and caramel to a microwave safe bowl. Microwave for 1-2 minutes, stirring every 30 seconds, until the peanut butter has melted into the caramel sauce. Stir well.
Drizzle the peanut butter sauce over the baked brownies. Cool completely before cutting and serving.