A quantum interference transistor comprising a thin metal film having a protrusion and a thin insulating layer between the metal film and protrusion. A potential barrier is formed in the region beneath the protrusion as a result of quantum interference caused by the geometry of the film and protrusion. A voltage applied between the electrically isolated protrusion ("island") and the thin film leads to a change in the electron wave function of the island which in turn leads to a change in the Fermi level of the metal film in the entire region beneath the protrusion. Consequently, a potential barrier may or may not exist depending on the applied voltage, thus providing the present invention with the transistor-like property of switching between open and closed states.