Heat semi-sweet chocolate chips in a double boiler or heavy saucepan over low heat, stirring constantly, until smooth.
To microwave, place chocolate in a microwave proof dish and melt 1/2-1 cup chips on medium (50%) 3-4 1/2 minutes. Stir until smooth. Dip pretzels with a fork and remove to wax paper. Refrigerate uncovered until chocolate is firm, about 30 minutes. Store, loosely covered in a cool, dry place or freeze in an airtight container.