The drain-current enhancement of the mechanically strained strained-Si NMOSFET device is investigated for the first time. The improvements of the drain current are found to be /spl sim/3.4% and /spl sim/6.5% for the strained-Si and control Si devices, respectively, with the channel length of 25 /spl mu/m at the external biaxial tensile strain of 0.037%, while the drain-current enhancements are /spl sim/2.0% and /spl sim/4.5% for strained-Si and control Si devices, respectively, with the channel length of 0.6 /spl mu/m. Beside the strain caused by lattice mismatch, the mechanical strain can further enhance the current drive of the strained-Si NMOSFET. The strain distribution due to the mechanical stress has different effect on the current enhancement depending on the strain magnitude and channel direction. The smaller current enhancement for strained-Si device as compared to the control device can be explained by the saturation of mobility enhancement at large strain.