Provided are a semiconductor device, a display panel, and a display device including the same. The semiconductor device includes a lower electrode on one side of a substrate, a spacer on another side of the substrate, a middle electrode on the spacer, a lower channel layer on portions of a sidewall of the spacer, the middle electrode, and the lower electrode, a lower gate insulating layer on the lower channel layer, a common gate electrode on the gate insulating layer, an upper gate insulating layer on the common gate electrode, an upper electrode on the spacer and the upper gate insulating layer of the middle electrode, an upper channel layer connected to the upper electrode and disposed on a sidewall of the upper gate insulating layer, and a contact electrode connected to a portion of the upper channel layer and passing through the lower gate insulating layer and the upper gate insulating layer outside the common gate electrode so as to be connected to the lower electrode.