A semiconductor device includes: a semiconductor substrate; a silicon pillar provided perpendicularly to a main surface of the semiconductor substrate; a gate dielectric film that covers a portion of a side surface of the silicon pillar; an insulator pillar that covers remaining portions of the side surface of the silicon pillar; a gate electrode that covers the silicon pillar via the gate dielectric film and the insulator pillar; an interlayer dielectric film provided above the silicon pillar, the gate dielectric film, the insulator pillar, and the gate electrode; and a gate contact plug embedded in a contact hole provided in the interlayer dielectric film, and in contact with the gate electrode and the insulator pillar. A film thickness of the insulator pillar in a lateral direction is thicker than a film thickness of the gate dielectric film in a lateral direction.