The model for simulating high‐frequency capacitance‐voltage characteristics of amorphous/crystalline heterojunctions has been developed, where the high frequency indicates a frequency higher than the reciprocal of the dielectric relaxation time of the amorphous semiconductor. The physical background of the space‐charge density of the amorphous film and the built‐in voltage of the heterojunction, which are experimentally obtained from the heterojunction‐monitored capacitance method, is discussed using the calculated results.