Hot Carrier Injection (HCI) is a critical reliability concern especially for NMOSFET in IC. The drain current (Id) shift of NMOS at high Vds (drain stress) and low Vgs (gate stress) conditions was investigated in this paper. We found that the drain current (Id @ Vgs = 0.62V, Vds = 5.5V) increased versus time at the stress conditions of Vgs = 0.62V, Vds = 5.5V while Idsat degraded at high Vds and low Vgs stress conditions. The dominant mechanism for this phenomenon is that the positive-charged traps generated in the gate oxide near the drain region. The experiments for process improvement showed that the holes injection of NMOSFET can be reduced by the proper annealing temperature of SiN and LDD (light doped drain) doping process.