Pour the chocolate syrup into a medium microwave safe bowl and microwave 2 minutes on high. Do not allow to boil. Stir peanut butter into hot chocolate until smooth. Allow to cool to room temperature.
Line the bottom of a 9x13 inch dish with 8 1/2 ice cream sandwiches. Spread half the whipped topping over the sandwiches. Spoon half the chocolate mixture over that. Top with half the peanuts. Repeat layers.
Freeze until firm, 1 hour. Cut into squares to serve.