The structure of the nanograting channel MOSFET was optimized by simply rounding the corners of the nanogratings. The current drivabilities of the optimized nanograting channel MOSFETs were enhanced by about 20% and 50% for both n-channel and p-channel MOSFETs, respectively. The mobility changes were analyzed on the basis of channel stress as well as theoretical change of mobilities by various surface orientations. The internal compressive stress of 0.23% was measured in the channel. By suppressing the electric field increase at the corner edge of the nanograting channel to less than 10%, the fabricated rounded nanograting MOSFETs achieved lifetimes of NBTI and TDDB as long as those of conventional planar devices.