Narrow-channel n-MOSFET's with recessed LOGOS (R-LOGOS) isolation structure exhibits less hot carrier-induced degradation than wide-channel n-MOSFET's, but the degradation mechanism of both devices is the same, This new finding is explained bg the fact that in deep submicron MOSFET's with ultra-thin gate oxide, the dominant factor deciding the degradation behavior in narrow- and wide-channel devices is the vertical electric field effect rather than the mechanical stress effect.