Abstract The properties of defects in as-grown p-type zinc germanium disphosphide (ZnGeP 2) and the influence of electron irradiation and annealing on the defect behavior were studied by means of electron paramagnetic resonance (EPR) and photo-EPR. Besides the well-known three native defects (V Zn, V P, Ge Zn), an S=1/2 EPR spectrum with an isotropic g=2.0123 and resolved hyperfine splitting from four equivalent I=1/2 neighbors is observed in electron-irradiated ZnGeP 2. This spectrum is tentatively assigned to the isolated Ge vacancy. Photo-EPR and annealing treatments show that the high-energy electron irradiation-induced changes in the EPR intensities of the zinc and phosphorus vacancies are caused by the Fermi level shift towards the conduction band. Annealing of the electron-irradiated samples induces a shift of the Fermi level back to its original position, accompanied by an increase of the EPR signal associated with the V Zn − and a proportional increase of the EPR signal assigned to the V P 0 under illumination ( λ<1 eV) as well as generation of a new defect. The results indicate that the EPR spectra originally assigned to the isolated V Zn − and V P 0 are in fact associated defects and the new defect is probably the isolated phosphorus vacancy V Pi.