The phenomenon and mechanism of hot-carrier-induced on-resistance (R on ) degradation for the n-type lateral diffused metaloxide-semiconductor (MOS) transistors stressed under various gate voltages (V g ) are investigated. R on degradation of the device is found to be attributed to the interface state (N it ) generation in the N À drift region. Moreover, R on degradation is almost identical for the devices stressed under medium V g and high V g , despite the fact that bulk current of the device is much greater at high V g bias. Such an anomalous R on degradation is suggested to be the result of two combined factors: the magnitude of impact ionization rate and N it generation efficiency.