Wash and dry the pears. Prepare a large bowl with water and lemon juice (1 tbsp lemon juice for every quart of water). This will keep the pear slices from browning and adds a little more flavor to the pears.
Prepare another small bowl with the cinnamon and sugar mixture and set aside.
Slice each pear using a mandoline if you have one. You can also use a knife, but I find the mandoline gives you nice even slices that are perfect for dehydrating.
Place the slices in the bowl of lemon water so they don't brown while you are prepping.
Once you have all of your pears sliced, place each piece on the dehydrator rack until the entire level is full. Sprinkle with cinnamon and sugar if desired and continue until all of your racks are full.
Place the lid on the dehydrator and set it to 135ºF. It will take anywhere from 6-10 hours for the pears to fully dehydrate. Start checking them around 6 hours. You want them to be dry, crisp, and no mushy spots. They may be slightly leathery and should crisp up when cooled.