Effects of inductively coupled plasma (ICP) treatment on Fermi level pinning on the surface of Si0.83Ge0.17 was studied by current–voltage and x-ray photoemission spectroscopy measurements. ICP treatment induced the growth of silicon oxide, suggesting that Si vacancies are generated under the oxide. From linear fitting of Schottky barrier heights with metal work functions, it was found that surface state density increased from 6.60×1012to1.13×1013∕cm2eV by the ICP treatment, leading to the pinning of surface Fermi level about EC∼0.53eV. From this, it is suggested that the Si vacancies are the main surface states in pinning Fermi level on the ICP-treated surface.