Abstract: In this paper, the photoluminescence spectra of n-GaAs and n-InP single crystals as well as epitaxial n-InP have been investigated. The electrical properties were measured by means of c-v. It was determined that the residual acceptor impurities are dominantly C and Si in the undoped GaAs. By ion implantation with Si at room temperature, followed by annealing treatment, it has been proved that the 1.403eV peak of the spectrum in GaAa is related with Si and V_As. Incorporated with the results of the chemical analysis as well as the ion probe, the investigation of the spectra for the undoped n-InP crystals shows that the -1.38eV peak of the spectrum is caused by C acceptor; 1.08 and -1.2eV speaks are connected with V_P and V_In respectively.