Ab initio calculations, based on pseudopotentials and the density-functional theory, have been made to investigate the equilibrium atomic geometry, electronic states, and bonding of the H2S molecule on the InP(110), GaAs(110), and GaP(110) surfaces within a dissociative adsorption model. In general, the adsorption of H2S on the three semiconductors shows similar behavior. The calculated average distances between the topmost InP, GaAs, and GaP layer and the sulfur atom are 1.87, 1.67, and 1.65 Angstrom, respectively. in all the cases studied here, the fundamental band gap is free of surface states, with an occupied surface stare close to the valence-band maximum. The calculated electronic states are in agreement with reported angle-resolved photoemission data. [S0163-1829(98)04208-8].