PURPOSE:To enhance the performance in simplified process by a method wherein a dielectric film is formed on an Si substrate and then an upper electrode is formed on the dielectric film. CONSTITUTION:The title thin film capacitor 2 is provided with an Si substrate 4 and a dielectric film formed on the surface of the Si substrate 4. On the other hand, an upper electrode 8 is laminated on the surface of the dielectric film 6 while a lower electrode 10 is laminated on the rear surface of the substrate 4. The laid substrate 4 in specific resistance not exceeding 0.1OMEGAcm fills the role of the lower electrode 10. Besides, the dielectric film 6 is a mixed layer comprising an Si oxide and a metallic oxide, a reaction product layer or a laminated layer structure of these layers. In such a constitutution, the substrate 4 becomes a part of the electrode 10 so that the dielectric layer 6 need not be laminated directly on the electrode 10 to simplify the process. Furthermore, the substrate 4 is thermally oxidized to form an SiO2 film thereby enabling the performance to be enhanced such as the augmented breakdown strength and finer-formed film.