The capacitance and chemical composition of the anodic films formed on Alloy 600 (UNS NO6600) and Alloy 690 (UNS NO6690) in 10% sodium hydroxide (NaOH) solution at 315degreesC were measured by electrochemical impedance spectroscopy and Auger electron spectroscopy. The stress corrosion cracking behavior of both alloys is discussed in terms of the film properties, such as semiconductivity and chemical composition.