We report the results of a photocapacitance study on stoichiometrically dependent deep levels in Sn-doped n-type InP (liquid encapusulated Czochralski) prepared by 4 h annealing at 700 degrees C under a controlled phosphorus vapor pressure. Photocapacitance measurements have revealed three dominant deep levels. The dominant deep levels which were located at 0.63 and 1.10 eV below the conduction band, and 0.74 eV above the valence band, were observed after annealing. The change of level densities was shown as a function of applied phosphorus vapor pressure. These deep levels were attributed to poor phosphorus composition. In order to investigate the optical transition mechanism of these deep levels, the excitation photocapacitance measurements have been carried out Amphoteric behavior due to Sn dopant before and after annealing is discussed.