[en] The electrical conductivity of single crystals of α-Al₂O₃ doped with Cr₂O₃ (0.03-2.5 wt%), NiO (0.75 wt%) plus Cr₂O₃ (0.03-0.15 wt%), and NiO (0.75 wt%) has been measured under 1 MeV electron irradiation at 300 K to investigate the effects of the concentration of impurity and of the depth of impurity levels in forbidden bands on the radiation induced conductivity (RIC). The RIC of Cr₂O₃ and/or NiO doped α-Al₂O₃ decreases with increasing concentration of Cr₂O₃ and/or NiO dopants. The electrical conductivity of 2.5 wt% Cr₂O₃ doped α-Al₂O₃ is smaller than any other doped materials tested. The dose rate exponent for Cr₂O₃ doped α-Al₂O₃ is smaller than that for NiO plus Cr₂O₃ doped material, due to deeper trapping centers of Cr (5.8 eV from the conduction band) than those of Ni (2.0 eV). Doping impurities with deep trapping centers are most effective for suppressing RIC