We have reexamined solid state thermionic emission cooling from first principles and report two key results. First, electrical and heat currents over a semiconductor/semiconductor thermionic barrier are determined by the chemical potential measured from the conduction band edge, not the energy band offset between the two materials as is sometimes assumed. Second, we show the upper limit to the performance of thermionic emission cooling is equivalent to the performance of an optimized thermoelectric device made from the same material. An overview of this theory is presented and instrumentation being developed to experimentally verify the theory is discussed. (8 References).