The adsorption and desorption of sulfur on a GaAs (001) surface was studied usinginsituAuger electron spectroscopy and reflection high‐energy electron diffraction (RHEED). The H2S ‐treated surface showed a (2×1) sulfur‐terminated structure, with the sulfur considered to be a few monolayers thick. RHEED patterns showed that the (2×1) reconstruction changed into an arsenic‐stabilized (2×4) structure when heated to 590 °C under an arsenic flux. A sulfur Auger signal on the H2S ‐treated surface was found to completely dissapear upon heating. These data show that H2S exposure is appropriate for preparing a sulfur‐terminated surface and that high‐quality crystal regrowth is possible on the surface after being heat treated.