The present disclosure provides a semiconductor structure includes a semiconductor layer having a first and a second surface, and an interlayer dielectric (ILD) defining a first metal gate and a second metal gate over the first and second surface, respectively. The first and second metal gate include a first SAC hard mask and a second SAC hard mask, respectively, wherein the first the second SAC hard mask have opposite stress to channel regions underneath the first and second metal gate, respectively. The present disclosure provides a method for manufacturing a semiconductor structure. The method includes forming metal gate recesses, forming metal gates and SAC hard masks in the metal gate recesses, respectively.