The present disclosure provides a semiconductor structure. The semiconductor structure includes a semiconductor layer having a surface, and an interlayer dielectric (ILD) defining a metal gate over the surface of the semiconductor layer. The metal gate includes a high-k dielectric layer, a capping layer, and a work function metal layer. A thickness of the capping layer sidewall distal to a corner of the capping layer, is substantially thinner than a thickness which is around center of the capping layer bottom. The present disclosure provides a method for manufacturing a semiconductor structure. The method includes forming a metal gate recess, forming a high-k dielectric layer, forming a first capping layer, forming a second capping layer on the first capping layer, removing or thinning down the first capping layer sidewall, and removing the second capping layer.