Cook sugar and 1/2 cup water in a small saucepan over medium heat, stirring occasionally, until sugar dissolves. Stir in peanuts, and cook 10 minutes or until sugar starts to crystallize on peanuts. Sprinkle pumpkin pie spice evenly over peanuts, stirring to coat. Spread nuts in a single layer on a lightly greased baking sheet.
Bake at 300° for 30 minutes, stirring every 10 minutes. Cool on baking sheet. Store in an airtight container.