Surface structures of clean and sulfur-treated GaP(111)A have been studied by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A GaP(111)A surface is reconstructed into a 2× 2 structure by Ar ion sputtering and annealing at 450°C. The 2× 2 structure is for the first time imaged by STM. A surface structure model for the structure is discussed in terms of the cation-vacancy model. The sulfur-treated surface shows a 1× 1 LEED pattern and the relative AES intensity of sulfur remains constant between 200-500°C. The coverage of sulfur on the GaP(111)A surface is estimated to be about 0.82 monolayers. The sulfur is desorbed at about 550°C where the LEED pattern was changed into a facet-like one. The different surface reconstructions (1× 1-S and 2× 2-S) on sulfur-treated III-V compound semiconductor (111)A surfaces are discussed in terms of the bond strength. [DOI: 10.1380/ejssnt.2009.213]