In this work, the perylene-monoimide/n-Si (100) Schottky structures have been fabricated by spin coating process. We have studied the capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of the Au/per-ylene-monoimide/n-Si diodes at 500 kHz before and after 60 Co γ-ray irradiation. The effects of 60 Co γ- irradiation on the electrical characteristics of a perylene-monoimide/n-Si Schottky diode have been investigated. A decrease both in the capacitance and conductance has been observed after 60 Co γ- irradiation. This has been attributed to a decrease in the net ionized dopant concentration that occurred as a result of 60 Co γ- irradiation. Some contact parameters such as barrier height (Φ B )interface state density (N ss ) and series resistance (R s ) have been calculated from the C-V and G-V characteristics of the diode before and after irradiation. It has been observed that the Φ B and N ss values are decreased after the applied radiation, while the Rs value is increased.