A powdery sample of CaH2heated to ∼730–790 K in a readily attainable high vacuum (∼1 ×10−7Torr) was found to emit thermal electrons (∼ 10−7–10−5A) and H−ions (∼ 10−15–10−12A, mass analyzed) from its surface (∼ 0.1 cm2). The work function of the sample and the desorption energy of H−were 4.8 ± 0.1 and 7.4 ± 0.2 eV, respectively. The latter fairly agreed with the value (7.1 ± 0.1 eV) derived theoretically by our simple model for the thermal negative ion emission. ©1995 American Institute of Physics.