Arrange baking racks in the top and bottom thirds of the oven. Preheat oven to 200ºF.
Prepare two rimmed baking sheets by lining them with parchment paper. Cut the top of the pear off just below the stem.
With a mandoline or sharp knife, thinly slice pears crosswise about 1/8-inch. Place pear slices in a single layer on prepared sheets, and sprinkle lemon juice on to every slice.
Mix sugar and cinnamon in a small bowl. Put contents into a sieve and sprinkle evenly over pear slices.
Bake for 2 hours or until pears are dry and crisp. Remove from oven and let slices cool completely before transferring to a sealed container for up to 3 days.