As accurate and rapid techniques for analytical performance prediction of thermionic plasma diodes are presently lacking, an IBM digital computer program has been developed to semi-empirically predict diode performance. Experimental curves of voltage versus current are presented for tantalum, molybdenum, and rhenium for a wide range of emitter and cesium temperatures. These are processed by the program to determine the optimum efficiency characteristics for various emitter temperatures. Graphical presentations of the processed data indicate the maximum obtainable efficiencies using any of the three emitter materials. The corresponding values of cesium temperature and diode voltage necessary to obtain this efficiency and the corresponding power densities are also presented.