Electrochemical luminescence of ZnGa2O4:Cr and ZnGa2O4:Co semiconductor electrodes was studied. Under cathodic polarization in Na2S2O8 electrolyte, these electrodes generated emission of ZnGa2O4 with a broad band from 350 to 650 nm together with red emission attributed to Cr3+ and Co2+. These emissions are explained by recombination between electrons and holes. Under anodic bias in Na2SO4 electrolyte, only the red emission was observed, accompanied with a sharp rise of anodic current at ca. + 12.5 V. The emissions were explained by collision excitation of Cr3+ and Co2+ emission centers owing to avalanche breakdown.