AlxGa1-xN semiconductor data were used to design a cathode with its layer thicknesses, doping level, and compositional grading specified. Semiconductor device theory was used to determine the thermal equilibrium condition in the cathode at various temperatures in order to compute the energy barrier for emitted electrons. The resulting current density was estimated from thermionic emission theory, and the results suggest that these cathodes could provide a current density of 100 A/cm(2) or more at temperatures below 600 K. Such cathodes should prove quite useful for many types of vacuum devices, particularly microwave tubes.