Electrical characteristics of P3HT/Aluminum organic/ inorganic heterojunction diodes were investigated V-I and capacitance-voltage (C-V) measurements. The V-I measurement exhibited current rectification inherent in the Schottky diode, suggesting their availabilities as rectification diodes in organic flexible circuits. C-V analysis indicated the fact that the depletion layer was generated in the P3HT film in the reversed bias condition. The flat band voltage analysis suggested that the interfacial charge affected the built-in potential of the diodes. Al/P3HT heterojunction is possible to be used as not only the rectification diodes but also gate junctions for junction type field effect or static induction transistors.