Combine 1 cup puffed rice cereal and 3/4 cup pretzel sticks, broken into bite-sized pieces. Melt 6 ounces semisweet chocolate chips in a microwave, stirring until smooth. Add 1/4 cup chunky peanut butter, stirring just until combined. Stir chocolate mixture into pretzel mixture; combine well. Drop 20 mounds onto a cookie sheet lined with parchment paper; chill until firm (about 10 minutes).