In this paper,secondary impact ionization(2II)induced degradation in 0.18μm channel length NMOSFETS is investigated by using gated diode technique.It is found that the interface trap generation is the dominant mechanism for hot carder degradation in advanced deep sub-micron NMOSFETS upon 2II stress.As a result，the interface traps induced the inversion layer mobility reduction is responsible for the electric parameter degradation in deep sub-micron NMOSFETS during 2II stress。