Abstract: A three terminal tunneling device analogous to a field effect transistor is disclosed. Preferred embodiments include a planar quantum well (52) with a gate insulator (56) and gate (58) on one surface and with a tunneling barrier (54) and source (62) and drain (60) on the other surface. The conduction current comprises electrons tunneling from the source (62) into the well (52) and then out into the drain (60). The gate (58) bias shifts the well subband levels up and down to establish and disrupt resonance for the tunneling from the source (62) into the well (52). Other preferred embodiments include interdigitated source and drain, multiple gates, multiple wells, and floating gates.