Thermodynamic data as well as physical and electrochemical studies demonstrate that the composition of the passive layer on chromium depends on the potential and the electrolyte pH. The electrochemical properties of electrodes were compared with the anodic behavior of chromium in borate buffer solutions. The feasibility of the solid‐phase transformation of a surface layer under anodic polarization was investigated. The conductivity type and deviation from the stoichiometric composition of the chromium oxide was determined in situ using the photopolarization method. Depending on the polarization potential, stoichiometric point defects in result in the p‐ or n‐type behavior of the oxide. The formula can be expressed as (or where ). Photopolarization measurements suggest that behave like a p‐type semiconductor at low anodic potentials, but it shows n‐type behavior at high anodic potentials. The transition from p‐type to n‐type conductivity is a pH‐dependent reversible process, occurring at potentials corresponding to the transformation of (p‐type) to (n‐type) via the solid‐state mechanism.