Place the Corn Chex in a large bowl, preferably with tall sides. Put the cereal to the side.
Whisk the powdered sugar and pumpkin pie spice together in a medium bowl, and set it aside.
In a separate, microwave-safe medium bowl, add the semi-sweet chocolate chips, butter, and peanut butter.Heat the bowl in the microwave in 30-second increments, stirring between each one until the mixture is smooth and somewhat thin. You don't want it too thick or it will clump up instead of coating the cereal.
Pour the chocolate over the cereal.Carefully fold the Chex and chocolate together until all of the pieces have been coated.
Spoon the mixture into a gallon-size plastic bag, and dump the powdered sugar mixture in with it. Shake the bag until all of the pieces are covered.
Pour into a large, shallow bowl or dish, and let it cool to room temperature so the chocolate sets. Sprinkle with a little extra pumpkin pie spice on top, if desired.
Enjoy!