A field-effect transistor includes a gate structure comprising a structure in which a first insulating layer, a first gate electrode, and a second insulating layer are sequentially stacked on a first conductive layer, the gate structure surrounding a first hole through the first insulating layer and exposing a part of the first conductive layer; a second conductive layer on the second insulating layer and surrounding a second hole connected to the first hole and exposing a part of the first conductive layer; a first gate insulating layer covering an inner wall of the gate structure exposed by the first hole; a semiconductor layer covering a part of the first conductive layer exposed through the first hole and the second hole, the first gate insulating layer, and the second conductive layer; a second gate insulating layer covering the semiconductor layer; and a second gate electrode filling the first and second holes.