Preheat oven to 400 degrees. In a 9x13 baking pan, add pretzels, melted butter, and 1/2 cup of the sugar. Mix well. Bake for 7 minutes. Let cool, then scrape pretzel mixture from the pan, breaking it up into small chunks.
Blend until creamy: cream cheese and 1/4 cup sugar.
Fold the pineapple and cool whip into the cream cheese mixture.