Line a baking sheet with parchment paper.
In a pot, combine sugar, corn syrup and water. Cook over medium-high heat until it boils.
Reduce heat to medium and carefully attach candy thermometer to the pot, make sure you thermometer is not touching the bottom of your pot.
Continue boiling, stirring occasionally, until candy thermometer reaches 250 degrees F (around 20-30 minutes).
Stir in peanuts and salt.
Cook until the mixture reaches 295 degrees F ( about 15-30 minutes).
Remove from the heat and immediately stir in the butter and baking soda. (You will it see it foam and change colors.)
Immediately pour the mixture onto the prepared baking sheet and spread with a spatula.
Cool completely and then break into bite-sized pieces. Store leftovers in an airtight container.