Surfaces shown by x‐ray diffraction measurements after fabrication to be TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2were subjected to vacuum thermionic work function and thermal stability measurements. Subsequent x‐ray diffraction stoichiometry checks showed that only ZrC and Mo2C remained stable after many hours at thermionic emission temperatures. TaB2decomposed to TaB+B when a diffusion barrier of TaC was provided under the TaB2; the three disilicides decomposed to lower silicon content silicides. The vacuum work functions measured after outgassing were TaB2(4.32 eV), ZrC(3.70 eV), Mo2C(4.74 eV), MoSi2(4.73 eV), TaSi2(4.71 eV), and WSi2(4.62 eV), subject to some temperature dependencies, as described.