In this study, electron emission model is investigated for heavily phosphorus‐doped n‐type diamond having positive electron affinity surface. Ultraviolet photoelectron spectroscopy (UPS) is conducted to determine the band structure of the diamond. In addition, combined UPS and field‐emitted electron spectroscopy is carried out in order to determine the energy level, from which electrons are emitted. The combined spectroscopy suggests that electrons are emitted from the conduction band of the diamond, and the emission mechanism is dominated by electron tunneling through surface potential barrier.