In this paper,the hot-carrier effect in grooved gate NMOSFET and the device degr adation induced by it were simulated using device simulator MEDICI,and compared with those of counter conventional planar device.The hot-carrier effect and the device degradation were explained using the distribution of some internal physic al parameters.The simulation results indicated that hot-carrier effect was stron gly suppressed in grooved gate MOSFET,while grooved gate MOSFET's performance wa s sensitive to hot carrier.