A study of the long-term stability of etching, photowashing, and sulfide passivation [using (NH4)(2)S] treatments performed on GaAs surfaces using photoreflectance spectroscopy is reported in this paper. Dramatic changes in the intensity of excitonic features of bulk n-GaAs qualitatively show much greater stability of sulfide-passivated than either etched or photowashed surfaces. We have also quantified the electric field in structures containing a thin, undoped GaAs layer over a highly doped n-GaAs buffer layer using strong Franz-Keldysh oscillations present in photoreflectance measurements. The results show a gradual degradation of the effects of etching and photowashing GaAs surfaces over a period of several months, while sulfide-passivated samples remain stable and, in some sense, "unpinned" over this same time period.