The junction capacitance for a carbonaceous thin‐film/n‐type silicon layer photovoltaic cell made by chemical vapor deposition of 2,5‐dimethyl‐p‐benzoquinone on a silicon substrate at 500 °C was measured, and an energy band diagram for this junction was sought out. The result confirms that the carbonaceous thin‐film/n‐type silicon junction is a heterotype junction. Its junction barrier is about 0.54 eV. This junction shows a depletion layer of about 1.1 &mgr;m in thickness at zero bias voltage, and most all of which was established in the silicon substrate. A work function of about 5.0 eV for the carbonaceous film was estimated based on the energy‐band diagram of this junction. ©1996 American Institute of Physics.