Spray a 15 X 10-inch baking sheet and metal spatula with cooking spray; set aside.
Combine syrup, sugar, water and butter in a heavy 3-quart saucepan. Cook over medium heat, stirring frequently, until sugar dissolves and mixture comes to a boil.
Cook without stirring until temperature reaches 280°F on a candy thermometer or small amount of mixture dropped into very cold water separates into threads which are hard but not brittle.
Gradually stir in peanuts; continue cooking, stirring frequently, until temperature reaches 300°F or small amount of mixture dropped into very cold water separates into threads which are hard and brittle. Remove from heat; stir in baking soda. Mixture will foam and become lighter in color.
Immediately pour mixture onto cookie sheet. With metal spatula, spread mixture evenly to edges. Cool and break into pieces.