In this paper, semiconducting behavior of temporarily protective oil coating on the surface of AISI 304 stainless steel in 5% Na2SO4 solution under corrosion potential was studied by utilizing potential-capacitance method and Mott-Schottky analysis. It was pointed out that there existed semiconducting behavior of temporarily protective oil coating during its degradation. With increasing of immersion time, temporarily protective oil coating transformed from p-type semiconductor at the early stage of immersion to n-type semiconductor. N-D and N-A of oil coating in different transition process were also calculated. (C) 2004 The Electrochemical Society.