Grease one 10x15 inch baking pan.
In a large saucepan over medium heat, combine the sugar, corn syrup and water; bring to a boil, stirring constantly until sugar is dissolved.
Continue to cook, without stirring until a candy thermometer reads 300 degrees F (150 degrees C).
Remove from heat; stir in butter, vanilla and baking soda. Add cereal and cashews; pour into prepared pan and allow to cool. Break into pieces and store in air tight container.