This article describes the admittance-frequency feature of a class of SnO 2 •CoO-based polycrystalline ceramics with high nonlinear current-voltage characteristics ͑nonlinear coefficients above 50͒. Broad relaxation peaks caused by the presence of deep trap states were characterized based on the admittance response of different systems doped with La 2 O 3 , Pr 2 O 3 , and CeO 2. The calculation of the energy of this deep trap level revealed not only that all the compositions share the same value but also that this value could be attributed to an oxygen vacancy or to Co Sn like defects. The values of barrier height and density of states obtained from a capacitance-voltage analysis are in good agreement with the nonlinear coefficients. The highest nonlinear coefficients are found in compositions with greater barrier height values and higher density of deep trap states at the grain boundary interface.