Experimental measurements have shown that uniform and stable electron emission is obtained from metallic planar surfaces covered with an ultra-thin wide band-gap semiconductor (UTSC) layer, with a threshold of the applied field in the range of 50 V mum(-1) and at 300 K. Numerical simulation analysis of a serial two-step mechanism model has been developed. The theoretical results confirm the main experimental characteristics and showed that a band bending of approximate to 5 eV is obtained for an UTSC layer thickness in the range of 3-7 nm.