The total concentration of ionized impurities in silicon implanted GaAs was estimated from carrier concentration and mobility values obtained by Hall effect measurements together with published compensations. We have demonstrated that the calculated profiles(ND++NA−)are in good agreement with that of the silicon atomic distributions obtained by secondary-ion-mass spectroscopy. We have observed that a large concentration of gallium vacancies are injected into the sample during a 900 °C anneal for 1000 s using a Si3N4cap. ©1997 American Institute of Physics.