Interface characteristics have a very important influence on the performance of thin film devices.ITO/PTCDA/p-Si thin film device was fabricated with vacuum evaporation and sputter deposition method.The surface and interface electron states of ITO/PTCDA/p-Si were investigated using X-ray photoelectron spectroscopy(XPS) and argon ion beam etch technology.Results indicate that at the interface of ITO/PTCDA/p-Si,diffusion occurs between not only ITO and PTCDA films but also PTCDA and Si substrate.Moreover,chemical shifts exist in the XPS spectra of each atom,and the chemical shifts of C1s and O1s are most remarkable.