Oxide films up to 2500 A˚ thick have been grown by anodization of GaAs in the negative glow region of a dc oxygen discharge. Using Auger analysis, as‐grown samples were found to contain excess Ga in the bulk of the film and excess As in a wide oxide‐GaAs interface region. Preliminary measurements indicate that plasma anodic films grown on bothp‐ andn‐type GaAs exhibit electrical properties similar to films formed by liquid anodization.