A silicon quantum wire transistor. A silicon substrate is sub-etched leaving a thin ridge (.ltoreq.500 .ANG. tall by .ltoreq.500 .ANG. wide) of silicon a quantum wire, on the substrate surface. An FET may be formed from the quantum wire by depositing or growing gate oxide and depositing gate poly. After defining a gate, the source and drain are defined. Alternatively, an optically activated transistor is formed by defining an emitter and collector and providing a path for illumination to the wire.