Semiconductor properties of the passive films formed on 316L and 2205 stainless steel were studied by Electrochemical Impedance Spectroscopy (EIS) in the high-temperature acetic acid. The results showed that the corrosion resistance of 2205 was higher than that of 316L, and the passive films formed on 316L and 2205 stainless steel showed p-type and n-type semiconductor behavior, respectively. Destruction and self-repairing of passive films were studied by using the constant current polarization method. The results showed that for 316L, the self-repairing process would occur when the destruction was lower than the critical extent or it would not do; for 2205, the self-repairing process only happened in a short time when the destruction was in the same extent as 316L.acetic acid, corrosion, semiconductor, stainless steelThe formation, rupture and pitting process of the passive film on stainless steel are determined by the transferation of electron and ion. The charge transmission is driven by the electric field, which is influenced by the electronic structure of passive film. Therefore, the corrosion resistance of stainless steel is closely related to the semiconductor electronic properties of the passive film on its surface [1,2] . Many advanced surface treatment techniques, such as ion beam, electron beam and laser beam, have been developed to modify the passive film with an attempt to enhance the corrosion resistance of stainless steel [3] . Hu et al. [4] proposed an electrochemical surface treatment which could substantially enhance the corrosion resistance of stainless steel. The reason was due to the modification of passive film after treatment in terms of semiconductor property. Zhang et al. [5] studied the semiconductor properties of the passive film formed on 304 stainless steel by use of EIS and photo-electrochemical technique in 0.5 mol/L Na 2 SO 4 solution, and investigated the semiconductor property of the passive film through Mott-Schottky analysis. Li et al. [6] studied the formation of the passive film on Fe and its alloys in neutral solution by using EIS and electrochemical noise technique. The results showed that the electronic nature of the passive film was affected by its formation potential, media types and so on. Hakiki et al. [7] studied molybdenum stainless steel with the method of MottSchottky curves and photoelectricity reaction. The results showed that the passive film on molybdenum stainless steel showed n-type semiconductor behavior, and the donor concentration was significantly decreased with the addition of Mo.The self-repairing abilities of the passive films on 316L and 2205 stainless steel were investigated after suffering different degrees of damage in this work. The semiconductor properties of the passive films formed on their surfaces were studied by using Mott-Schottky theory. The enhancement mechanics of corrosion resistance of stainless steel was discussed in terms of the semiconductor properties of the passive films.