It is shown that the electrical properties of undoped single crystals of ZnGeP2 and CdSiP2 are due to their intrinsic defects. Thermal treatment in the vapour of the components or ion implantation allows to obtain a wide range variation both, of the carrier density and polarity. Acceptor defects in ZnGeP2 are caused by zinc vacancies, their energetic position is Ev + 0.72 eV. Acceptor defects in CdSiP2 form level at Ev + 0.45 eV. Predominating donors in CdSiP2 and ZnGeP2 are phosphor vacancies. Their energy position in CdSiP2 is at Ec — 0.63 eV. The influence of germanium on the electrical properties of ZnGeP2 is not revealed, while silicon is amphoterically soluted in CdSiP2.