A field effect transistor includes an active layer and a capping layer sequentially stacked on a substrate, and a gate electrode penetrating the capping layer and being adjacent to the active layer. The gate electrode includes a foot portion adjacent to the active layer and a head portion having a width greater than a width of the foot portion. The foot portion of an end part of the gate electrode has a width less than a width of the head portion of another part of the gate electrode and greater than a width of the foot portion of the another part of the gate electrode. The foot portion of the end part of the gate electrode further penetrates the active layer so as to be adjacent to the substrate.