High quality SiO2films were deposited by plasma‐enhanced chemical vapor deposition on GaAs wafers which received different surface treatments. It was found that metal‐oxide‐semiconductor (MOS) capacitors which received surface nitridation were unstable under high‐temperature anneal (600 °C). These instabilities are interpreted in terms of free As precipitates at the interface. When, instead, a thin Si layer was deposited on the GaAs surface, stable interfaces were obtained at 600 °C. These MOS capacitors appear to show both deep depletion and inversion.