Deep majority-carrier traps have been studied by means of deep level transient spectroscopy (DLTS) in as-grown Zn3P2 polycrystals (p-type) grown either by sublimation or by iodine chemical transport using an automated digital DLTS system. Three main deep hole traps are present in both kinds of Zn3P2: hole traps with activation energy of 0.20±0.01 eV 0.36±0.005 eV, and 0.73±0.01 eV from the top of the valence band. In a few sublimation-grown samples a 0.48±0.02 eV hole trap is detected. The concentration of these levels, however, exhibits a very strong dependence on the thermal history of the samples, since Mg from the Schottky contact easily diffuses into the bulk above 50 °C and affects the concentration of the levels.