The transpassive dissolution mechanism of AISI 316L stainless steel was studied using electrochemical impedance spectroscopy (EIS). A generalized model of the transpassivity is proposed. The transpassive film is modeled as a highly doped n-type semiconductor-insulator-p-type semiconductor (n-i-p) structure. Injection of negative defects at the transpassive film/solution interface results in their accumulation as a negative surface charge. It alters the non-stationary transpassive film growth rate controlled by the transport of positive defects (oxygen vacancies). The model describes the process as dissolution of Cr as Cr(VI) and Fe as Fe(III) through the transpassive film via parallel reaction paths. (C) 2009 Elsevier Ltd. All rights reserved.