A structure and method for preventing minority carriers caused by an alpha particle, or the like, from drifting into storage regions and causing a false data bit. In a high density MOS circuit, a single alpha particle including one originating within the substrate or circuit package can generate enough carriers to give a false data bit. A minority carrier reflective barrier is employed to prevent substantial numbers of minority carriers from drifting into the active layer. In the presently preferred embodiment, this barrier is formed by ion implanting the upper surface of the substrate.