Atomic geometry, electronic states and bonding of H2S-adsorption on the InP(110) surface are studied by using ab initio calculations, based on the pseudopotentials and density functional theory. The adsorption of the molecule removes the relaxation of the clean InP(110) surface. The calculated average distance between the topmost InP taper and the sulphur atom is 1.87 Angstrom. which is in agreement with an X-ray standing-wave study. We also find that the fundamental band gap is free of surface states, indicating that the adsorption of H2S passivates the InP(110) surface, Furthermore, the calculated surface states agree well with angle-resolved photoemission measurements. (C) 1998 Elsevier Science B.V.