The held emission current from boron-doped polycrystalline diamond films was investigated. The current measurements were carried out as a function of voltage and temperature. The motivation for the current-temperature measurements was to assess the thermal stability of the diamond emitters and gain some insight into a possible emission mechanism. Results from the current-temperature measurements found that the emission current in the N-doped material had an exponential dependence on temperature of 0.16 eV. For the B-doped samples, the emission current appeared to be independent of temperature. Assuming a work function for B-doped diamond greater than 1 eV, the current-voltage measurements revealed that the electron emission sites had field enhancement factors greater than 1000. This combined with the temperature independence results led to the conclusion that for B-doped polycrystalline diamond films, electron emission is from the valence band.