A second-breakdown phenomenon (It2) in a drain-extended n-type metaloxidesemiconductor (DENMOS) is associated with complex triggering of a parasitic bipolar transistor. Full comprehension of the problem requires 3-D modeling; however, there is even deficiency in the understanding of the phenomenon occurring in the 2-D cross-sectional plane. We present experiments and models to understand the physics of bipolar turn-on and its impact on the onset of space-charge modulation in a DENMOS device. We present a detailed analysis of the current paths involved during the bipolar turn-on. We show that a strong snapback is triggered due to coupling of the parasitic bipolar turn-on in a deeper region of the p-body and avalanche injection at the drain junction. Furthermore, we show that the ballast resistor formed in the drain region due to current crowding of electrons under high-current conditions can be modeled through a simplified 1-D analysis of the n+/n- resistive structure. © 2006 IEEE.