A model is proposed to explain the electron‐emission properties of metals coated with thin evaporated films of BaO. The model considers the BaO‐metal interface to be rectifying, and the interior of the BaO layer to have a large density of donor sites. Experimental data from both this laboratory and the literature, pertaining to both thermionic and photoelectric emission properties, are shown to be consistent with predictions based on the proposed model. A striking enhancement is reported in the photoemission from BaO‐coated cathodes that are either bombarded by electrons or heated. The theory developed explains the observed dependence of work function on BaO‐layer thickness, the observed independence of emission work function on the work function of the substrate metals, and the effects of nonuniform BaO deposits on electron‐emission properties.