A cathode consisting of AlxGa1-xN is theoretically investigated. Spatial variations of Al fraction are used to provide a structure which transports electrons from n-type GaN material to Al0.75Ga0.25N material which exhibits negative electron affinity. The simulations indicate the emitted electron current density corresponding to various applied fields. The results for structures in which a 75-nm-thick layer of compositionally graded AlxGa1-xN sits upon a 100-nm-tkick layer of GaN indicate that: at room temperature a thermionic emission current density on the order of 100 A/cm(2) can be expected for an applied field of about 75 V/mu m. These new results indicate that AlxGa1-xN compositionally graded cathodes should be useful for vacuum microelectronic devices.