1. An electrical circuit comprising: a pair of three-terminal electronic control devices each comprising a body of semiconductor material defining a primary current path and which is essentially amorphous in one state theroef, outer and inner primary electrodes on opposite sides of the body of semiconductor material across which a load circuit including a source of voltage is to be applied, and electron emitting means interfaced with said body of semiconductor material on the side of said inner primary electrode remote from the outer primary electrode, said electrode emitting means including an electron emitting electrode, a thin insulating layer separating said electron emitting electrode from said inner primary electrode, said inner primary electrode being constructed to provide an electric field between it and said electron emitting electrode which causes electrons to flow from said electron emitting electrode and through said thin insulating layer to pass into said body of semiconductor material when a voltage of proper polarity is connected between said inner primary electrode and said electron emitting electrode; a pair of voltage input terminals; the pair of electronic control devices being connected in back-to-back relation between said voltage input terminals in that the inner primary electrode of one of said devices and the outer primary electrode of the other device are coupled to one of said voltage input terminals and the inner primary electrode of said other device and the outer primary electrode of said one device are coupled to the other voltage input terminal, whereby current can readily flow in different directions between the voltage input terminals; means connecting a control signal source to the electron emitting electrode of one of the devices to control the conduction between the primary electrodes thereof; and means connecting a control signal source to the electron emitting electrode of the other device to control the conduction thereof between the primary electrodes thereof.