Preheat the oven. Preheat your oven to 225°F (107°C). Line one or two large baking sheets with parchment paper.
Prepare the apples. Wash and dry the apples. Remove the cores and seeds, then slice the apples very thinly, about ⅛ inch thick. You can leave the peel on.
Make the cinnamon sugar. Add the granulated sugar and cinnamon to a small bowl. Stir until evenly combined.
Arrange the apples. Place the apple slices in a single layer on the prepared baking sheets. Avoid overlapping the slices so they can dry evenly.
Add the oil and cinnamon sugar. Lightly brush or spray the apple slices with the oil. Sprinkle the cinnamon-sugar mixture evenly over the slices. For more flavor, carefully flip the slices and season the other side as well.
Bake. Place the baking sheets in the oven and bake for 1½ to 2½ hours, depending on the thickness and moisture content of the apples.
Flip halfway through. Carefully flip the apple slices about halfway through baking. Rotate the baking sheets if needed so the apples bake evenly.
Check for doneness. Continue baking until the apples are dry and lightly crisp around the edges. The exact baking time will vary depending on the apples and your oven.
Cool completely. Remove the apple chips from the oven and let them cool completely. They will become firmer and crispier as they cool.
Serve. Enjoy the cinnamon sugar apple chips once completely cooled.