In this paper,the hot-carrier mechanism in grooved-gate MOS is analyzed at first .It is found that the hot-carrier effect reaches its highest generate rate under medium gate bias voltage of the three stress areas.Then,the characteristics of hot-carrier-effect in grooved-gate and planar PMOSFET are simulated using advanc ed 2-dimensional device simulator.The results show that the hot-carrier generate d in grooved-gate PMOSFET is far less than in planar PMOSFET,especially for the case of channel length in deep-sub-micron and super deep-sub-micron region.In or der to investigate the other influences of hot-carrier-effect immunity on device characteristics,the drift of gate and drain characteristics induced by differen t interface state is studied for grooved-gate and planar devices.It shows that t he drift induced by same interface state in grooved-gate MOSFET is far larger th an in planar device.This work lays a foundation for the research and design of n ovel very-small-size grooved gate CMOS devices.