A fin extends from, and is perpendicular to, a planar surface of a substrate. A self-aligned bottom source/drain conductor is on the substrate adjacent the fin, a bottom insulator spacer is on the bottom source/drain conductor adjacent the fin, and a gate insulator is on a channel portion of the fin. A gate conductor is on the gate insulator, a self-aligned top source/drain conductor contacts the channel portion of the fin distal to the bottom insulator spacer, a top gate length limit insulator is positioned where the channel portion meets the top source/drain conductor, and a bottom gate length limit insulator is positioned where the channel portion meets the bottom insulator spacer. The gate length of the gate conductor is defined by a distance between the gate length limit insulators.