an soi / sos thin film mos mesa architecture has its body / channel region extended beyond the source and drain regions and the impurity concentration is increased at a selected portion of the extended body region , so as to provide both a body tie access location which enables the body / channel region to be terminated to a prescribed bias voltage , and a channel stop region that is effective to functionally interrupt a current leakage path or ` parasitic ` n - channel that may be induced along sidewall surface of the p - type material of the body / channel region . in another embodiment , ionizing radiation - induced inversion of the sidewalls of the p - type body / channel region is prevented by an asymmetric sidewall channel stop structure formed in opposite end portions of the source region .