Oxide films grown by heat treatment on the 100 and 111 faces of GaAs have been studied by Raman backscattering. A spectrum consisting of the bulk LO and TO lines of GaAs and two additional lines labeled R1 and R2 is observed on all samples prepared at temperatures above 435° C. The additional modes are attributed to an interface region of perhaps several hundred angstroms thickness beneath the oxide film. This structure appears to be made unstable by chemical removal of the film. After the film is removed, the spectrum is annealed (returns to that of GaAs) in a matter of weeks at room temperature and in about 1 h at 400° C whether the annealing atmosphere is N2, O2, or forming gas. One of the modes, R2, appears to scatter as a scalar, i.e., a diagonal Raman matrix element. Spectra by the R1 mode on the other hand appear to be largely unpolarized or possibly slightly nondiagonal in character. Some speculations about the possible nature of the interface region are presented.