Place the Chocolate Chex cereal in a large microwave-safe bowl.

In a separate microwave-safe measuring cup or bowl, combine the packed brown sugar, butter or margarine, and light corn syrup. Microwave on High for about 2 minutes, stir carefully, and continue microwaving in short intervals until the mixture is bubbling and smooth.

Stir the baking soda into the hot caramel mixture until it is fully dissolved.

Pour the caramel over the cereal and stir gently until the pieces are evenly coated.

Microwave the coated cereal for about 3 minutes, stirring once each minute so the caramel stays distributed throughout the bowl.

Spread the hot mixture on waxed paper or parchment paper. Separate very large clusters as the crunch cools.

Melt the semisweet chocolate chips in the microwave using 30-second intervals, stirring between each interval until smooth.

Drizzle the melted chocolate over the cereal crunch. Let it cool for about 1 hour, then break it into serving-size pieces.