Thermionic emitters consisting of barium oxide dispersed throughout a body of porous tungsten can be successfully made if suitable compounds of barium are employed as the source of the oxide. Compounds such as the carbonate, which can oxidize tungsten and react to form Ba3WO6:3BaCO3+W→Ba3WO6+3CO,are unsuitable. However, if by various means, BaO is dispersed in tungsten, reaction occurs at operating temperature of the cathode to slowly generate free barium: 6BaO+W→Ba3WO6+3Ba, which diffuses to the surface and lowers the work function.Cathodes consisting of approximately 5 percent of BaO in W are capable of supplying continuous emission in excess of 100 amp/cm2, give equivalent dc and pulsed emission, and are highly resistant to damage by arcing, temporary poor vacuum, ion bombardment, and high temperatures.Emission current of approximately 8 amp/cm2was obtained at an operating temperature of 1000°C from a typical cathode of this type. The life of this cathode, at 1100°C, was in excess of 650 hours. Constants of the Richardson equation for a relatively inactive cathode were &fgr;=1.56 ev,A=0.6 amp/cm2/deg2.