The energy density of states in a Si grain boundary has been quantitatively determined for the first time. Since the deconvolution scheme used in this determination is a technique previously unapplied to real materials, the applicability of the model and the validity of the results were experimentally verified by comparing conductance and capacitance data. Additionally, a high‐voltage varistor characteristic (highly non‐Ohmic current) was observed. This shows for the first time that a simple grain boundary without intergranular additives is capable of a strong varistor behavior (nonlinearity coefficient &agr;≳20).