The effects of a gas‐phase polysulfide treatment on InP were studied by x‐ray absorption near‐edge structures (XANES) of both the sulfurL‐edge andK‐edge, and by x‐ray photoelectron spectroscopy (XPS). Some passivated InP samples were encapsulated with about 4 nm of remote plasma deposited silicon nitride, and the chemical structure of the sulfur atoms at the interface was again determined by angle dependentK‐edge XANES. Both XPS andL‐edge XANES confirmed the presence of indium to sulfide bonding on the surface exposed to gas‐phase polysulfide, and XPS confirmed the presence of more than one sulfide species. The angle dependence inK‐edge XANES indicated that most of the surface sulfur atoms had their sigma bonds oriented along the (110) azimuth with a polar tilt angle of about 40°–60°. It is thus plausible that these sulfur atoms terminated the indium atoms on InP (100) in the form of In–S–In bridging bonds along the (110) azimuth. Vacuum annealing was found to cause desorption of some surface sulfide species and conversion of the residual sulfide species into one sulfide species, and to enhance the XANES angle dependence which again indicated the presence of the In–S–In bridging bonds along the (110) azimuth. Further angle dependentK‐edge XANES analyses showed that such a sulfur bonding configuration was preserved even after the gas‐phase polysulfide passivated InP surface was capped with silicon nitride deposited by remote plasma chemical vapor deposition.