We present the surface characterization and the local electronic properties of archetypical p-type perylene-based semiconductor organic molecule of Perylene Tetra Carboxylic Dianhydride (PTCDA) thermally evaporated on a transparent conducting metal oxide surface. A modified indium tin oxide (ITO) surface was successfully obtained by employing a subsequent chemical and physical treatment. Physisorbed PTCDA molecules exhibited a stacked-grain structure covering completely ITO surface. Scanning tunneling spectroscopy (STS) spectra of physisorbed PTCDA molecules were performed. In contrast to the previous studies of the homolog n-type perylene derivative thin films, here we successfully extracted both of the outmost frontier energy levels by measuring the current-voltage characteristics of PTCDA molecules in an estimated tunneling resistance from 4.17 to 100 GΩ at room temperature. Using numerical derivative of the I-V spectra, we extracted the series of transport gap of PTCDA molecule are lies in the region of 4.70-4.87 eV.