Line a large baking sheet with parchment paper or a silicone baking mat and set aside.
Melt the coarsely chopped semi-sweet chocolate using a double boiler or microwave; if using the microwave, heat in 20-second bursts, stirring between each until smooth.
Combine the peanut butter chips and creamy peanut butter in a small heatproof bowl and melt at 50% power in 20-second increments, stirring after each, until completely smooth.
Pour the melted chocolate onto the prepared sheet and spread into a smooth, even layer with a rubber spatula.
Drizzle the melted peanut butter mixture in parallel lines over the chocolate, then drag a toothpick or knife through both layers to create swirls.
Refrigerate until the bark is completely set, about 30 minutes, then break into pieces of your desired size.