Time‐dependent dielectric breakdown lifetime of 5‐nm‐thick silicon oxide films in metal–oxide semiconductors (MOSs) fabricated by a new continuous ultra‐dry process was investigated. In this process, three fundamental stages in MOS diode fabrication—oxidation, amorphous‐Si electrode film formation, and annealing to crystallize the electrode film—are continuously performed in an ultra‐dry ambient with less than 100 ppb moisture concentration (humidity). The lifetime for the continuously ultra‐dry processed MOS diodes is considerably larger than that of conventional ones produced in an ambient with more than 100–200 ppm humidity. The stress‐induced positive charges that affect lifetime are mainly generated and trapped near both oxide interfaces. This indicates that the interface condition is probably improved by the present process.