On the samples of SEF wafers it has been shown that the thickness of oxide films and the surface oxidation conditions demonstrate strong effect upon the electron work function (EWF), measured under atmospheric conditions by technique of the static condenser with the ionized space. The EWF changes are connected with the water sorbed vapors, the quantity of which is determined by the oxide film structure and properties. It has been found that the EWF changes depending on the oxide film type can achieve ~ 20%.