In a bowl, combine pretzels, butter and 1/2 of the sugar. Press into a 9x13-inch baking pan. Bake at 400 degrees for 7 minutes. Cool.
Meanwhile, in a mixing bowl, beat cream cheese and remaining sugar until creamy. Fold in pineapple and whipped topping. Chill.
Before serving, break pretzel mixture into small pieces; stir into pineapple mixture.