The present invention relates to enhancing MOSFET performance with the corner stresses of STI. A method of manufacturing a MOS device comprises the steps of: providing a semiconductor substrate; forming trenches on the semiconductor substrate and at least a pMOS region and at least an nMOS region surrounded by the trenches; filling the trenches with a dielectric material having a stress; removing at least the dielectric material having a stress in the trenches which is adjacent to a position where a channel is to be formed on each of the pMOS and nMOS regions so as to form exposed regions; filling the exposed regions with a insulating material; and forming pMOS and nMOS devices on the pMOS region and the nMOS region, respectively, wherein each of the pMOS and nMOS devices comprises a channel, a gate formed above the channel, and a source and a drain formed at both sides of the channel; wherein in a channel length direction, the boundary of each exposed region is substantially aligned with the boundary of the position of the channel, or the boundary of each exposed region extends along the channel length direction to be aligned with the boundary of corresponding pMOS or nMOS region.