A plasmonic transistor device includes an electro-optic substrate and a conductive layer placed on said electro-optic substrate to establish an interface therebetween. The first conductive layer and electro-optics substrate are made of materials that are suitable for transmission of a surface plasmon along the interface. The conductive layer is further formed with a source input grating and a drain output grating, for establishing the surface plasmon. A means for varying the electro-optic substrate permittivity, such as a light source or voltage source, is connected to the electro-optic substrate. Selective manipulation of the varying means allows the user to selectively increase or decrease the substrate permittivity. Control of the substrate permittivity further allows the user to control surface plasmon propagation from the source input grating along the interface to a drain output grating, to achieve a transistor-like effect for the surface plasmon.