Electrical instabilities in films under high fields at elevated temperatures have been widely attributed to mobile ionic impurities, with sodium suspected as the most important ion. Phosphate glass treatments on are known to have a stabilizing effect. This paper reports neutron activation experiments to determine sodium contamination on and in steam‐grown films and also diffusion and drift experiments with tracer sodium. Phosphate glass‐treated films were included in the samples. films grown and handled under various conditions had sodium densities of , which could be easily removed or exchanged by washing and light etching. Densities remaining inside the 6000Aå films after washing and light etching were .Tracer diffusions into at 600°C produced profiles which were high near the surface and lower through the interior of the film, similar to those observed by neutron activation for unintentional sodium contamination. Phosphate glass layers on absorbed and stopped the sodium under similar conditions. With an applied field at elevated temperature (+4v, 1 min, 400°C) tracer sodium drifted through an film under gold dot electrodes, piled up at the interface, and carried a substantial part of the charge transported. There was no detectable diffusion in uncharged areas. A layer of phosphate glass applied over an film absorbed sodium and prevented it from drifting into the film under the gold dots.