A technique relates to a semiconductor device. An emitter electrode and a collector electrode are formed in a dielectric layer such that a nanogap separates the emitter electrode and the collector electrode, a portion of the emitter electrode including layers. A channel is formed in the dielectric layer so as to traverse the nanogap. A top layer is formed over the channel so as to cover the channel and the nanogap without filling in the channel and the nanogap, thereby forming a vacuum channel transistor structure.