Leakage currents in two different capacitors, metal-insulator-metal (MIM) and metal-insulator-semiconductor-metal (MISM), are examined. The leakage current of the MIM capacitors with a Nylon6-TiO2 nanocomposite film was larger than that for the devices with a poly(4-vinylphenol) (PVP) buffer layer stacked on top of the composite film by a factor of 3.6. When the organic active layer of pentacene is introduced for the MISM capacitor, the reduction ratio of leakage current by stacking the PVP buffer layer onto the composite film is found to get more pronounced as much as about a factor of 25. Such a significant difference of reduction ratio for the leakage current between the MIM and MISM capacitors results from the different polymorphs of pentacene which are critically dictated by the morphological surface of the underlying layer.