Diode structures of stacked devices and methods of forming the same are provided. Diode structures may include a substrate, an upper semiconductor layer that is spaced apart from the substrate in a vertical direction, an upper thin semiconductor layer protruding from a side surface of the upper semiconductor layer in a first horizontal direction, a lower semiconductor layer that is between the substrate and the upper semiconductor layer and has a first conductivity type, a lower thin semiconductor layer protruding from a side surface of the lower semiconductor layer in the first horizontal direction, a first diode contact that is electrically connected to the lower semiconductor layer, and a second diode contact that is electrically connected to one of the upper semiconductor layer and a portion of the substrate. The one of the upper semiconductor layer and the portion of the substrate may have a second conductivity type.