Combine first three ingredients in a glass microwavable bowl.
Add 1/2 teaspoon salt.
Cook on high power until mixture boils (about 2 minutes depending on microwave) Stir, then cook 2 minutes longer.
Remove bowl and stir in baking soda until the color changes to a light caramel and the mixture becomes light and fluffy.
With popped corn in a brown grocery bag, Pour hot syrup over corn Close bag and shake.
Cook in bag on high for about 2 minutes.
Remove bag, shake, and cook 1 minute.
Pour caramel corn out onto a cookie sheet or waxed paper, spread evenly to cool.