The structure and electronic states of an (NH4)(2)S-x-treated InP(1 1 1)A surface has been studied by using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), scanning tunneling microscopy (STM), and inverse photoemission spectroscopy (IPES). The sample annealed in ultra-high vacuum (UHV) condition at similar to 300-400 degrees C showed a 2 x 2-LEED pattern. Oval-shaped protrusions are observed in filled-state STM images. IPES intensity of the (2 x 2)-S surface at E-F +1-3 eV and +4-6 eV is decreased by the (NH4)(2)S-x treatment. Based on these results, a plausible structural model is discussed. (c) 2004 Elsevier B.V. All rights reserved.