Studies of chemical and electronic interaction at organic/inorganic interfaces are described; Electrochemical deposition of conducting polymers [poly(3-methylthiophene), polythiophene, poly(3-methylpyrrole), polypyrrole, poly(3-methylthiophene-co-pyrrole)] on an n-Si wafer does not give rise to high-quality p-n heterojunctions, but it is found that their junction properties are greatly improved by their electrochemical reduction (cathodic treatment). For example, the cathodic treatment of an as-grown poly(3-methylthiophene)/n-Si junction cell with rectifying ratio, gamma, of 1.4 x 10(1) and diode factor, n, of 2.6 gives a high quality junction with gamma = 1.7 x 10(4) and n = 1.2. The treatment involves not only the development of polymer films but the improvement in junction interface, since the treatment can contribute to the improvement only when conducted in the presence of polymer films. In order to understand this modification at the interface, the effects of cathodic treatment conditions (treatment potential and time) and the presence of an interfacial oxide. layer on the junction properties are investigated. As a result, it is revealed that the improvement is explained by a junction formation model described as the evolution of covalent bond formation at the interface; Further electrochemical studies reveal that such bondings are disrupted by hydrolysis and/or oxidation, and the bond disruption model is used to describe the degradation of the junctions in the air.