The epitaxial lift-off (ELO) process is utilized to produce thin-film III-V devices, while the substrate (GaAs wafer) on which the III-V structure was grown can be reused. However, so far the direct reuse of these GaAs wafers is inhibited by the remnants on the wafer surface that cannot be removed in a straightforward fashion utilizing general cleaning methods. Therefore, etching of GaAs wafers in hydrofluoric acid was investigated by microscopic techniques, profilometry and X-ray photoelectron spectroscopy. It was found that immediately after etching the wafer surface is covered by a brown layer of elemental arsenic. The thickness and uniformity of this layer depend on both illumination during etching and the HF concentration. During storage of the etched wafer the As layer is replaced by As2O3 particles. It is shown that oxide particles form only when the wafer is exposed to light in the presence of air. A model that explains the As formation and the subsequent particle formation is given.