A method of forming a gate-all-around device includes forming a gate electrode layer over a substrate, patterning the gate electrode layer to form a conical frustum-shaped gate electrode, etching the conical frustum-shaped gate electrode to form a through hole extending through top and bottom surfaces of the conical frustum-shaped gate electrode, and after etching the conical frustum-shaped gate electrode, forming a nanowire in the through hole in the conical frustum-shaped gate electrode.