Experiments are performed. which investigated the performance of a planar thermionic converter with molybdenum electrodes and 0.5 mm inter-electrode gap for low temperature, energy conversion applications. Results confirmed that for T-E 1773 K, the performance of the converter is superior to that with a tungsten emitter, when operated at near same conditions. The largest difference occurred at T-E similar to 1600 K and T-C similar to 1000 K. at which the maximum electric power density (3.0 W-e/cm(2)) is 70% higher than that of the converter with a W emitter, at more than double the output voltage (0.43 V vs. 0.21 V) and at lower cesium pressure (similar to105 Pa vs. 245 Pa). At T-E = 1700 K, T-C = 1000 K and T-E = 1600 K, T-C = 800 K, respectively, the maximum electric power density of the present converter is 25% and 50% higher and occurred consistently at lower cesium pressure and higher output voltage. At TE = 1673 K and T-C = 973 K, an electric power density of similar to3.22 W-e/cm(2) is measured at 0.49 V, P-Cs = 241 Pa, and an estimated conversion efficiency of 12.4%. For the same electrode temperatures, however, the estimated peak efficiency of 15.1% occurred at a significantly lower P-Cs (140 Pa), at which the measured electric power density = 2.27 W/cm(2).