Line a 15x10x1-in. baking pan with waxed paper and set aside.
In a microwave-safe bowl, melt semi-sweet chips; stir until smooth. Spread onto prepared pan. Refrigerate for 15 minutes or until firm.
In another microwave-safe bowl, melt white chips and butter; stir until smooth. Spread over semi-sweet layer. Drizzle with caramel topping; sprinkle with pretzels.
Refrigerate for 1 hour or until firm. Break into pieces.