Slice apples evenly using a mandolin slicer. Watch out for your fingers!
Seed the apple slices- seeds should fall out on their own by slightly bending the slice.
Lay out a single layer of the slices on the dehydrator panels and sprinkle with cinnamon sugar.
Set dehydrator temperature to 135° F. Add trays of apples and allow to dry for at least 11 hours, more depending on the humidity level of your zone. Check apples for dryness before removing- they should have some give to them, but no moisture.