Effect of silicon on the defect density of Fe-20Cr-xSi (x = 0, 1, 2) stainless steel alloys was investigated in deaerated pH 8.5 borate buffer solution at room temperature using Mott-Schottky analysis. Results showed that silicon was incorporated/dissolved in the passive film of Fe-20Cr-xSi (x = 0, 1, 2) alloys. Mott-Schottky analysis revealed that the addition of silicon decreased the acceptor density (N(A), V(Cr)(-3)), i.e., increased the Cr(+3) content of the passive film. Also the donor densities, shallow donor (N(D1), V(O)(+2)) and deep donor (N(D2), V(Cr)(+6)), of the passive films formed were decreased. XPS analysis confirmed the presence of Si in the passive film of Si containing alloys. This enriched silicon along with higher Cr(+3) concentration of the passive film, dictated its enhanced protectiveness and stability. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.083111jes] All rights reserved.