Line baking tray with parchment paper and set aside.
Combine sugar and cinnamon and mix well then set aside.
Slice oranges very thin using either a mandolin or a very sharp knife. The thinner the better.
Lay out orange slices on the baking tray.
Sprinkle slices with half of the quantity of cinnamon sugar. Save the rest for the other side of the oranges.
Place in a preheated oven at 200 and allow orange slices to slowly dehydrate.
Turn after 1 hour and sprinkle with balance of cinnamon sugar and cook for another 1 hour.
Once orange slices are nicely dried, remove from the oven and allow to cool.
Store in an airtight container.