A method of forming a semiconductor structure includes providing a semiconductor substrate comprising a first region and a second region, forming a first PMOS device in the first region wherein a first gate electrode of the first PMOS device has a first p-type impurity concentration, forming a stress memorization layer over the first PMOS device, reducing the stress memorization layer in the first region, performing an annealing after the step of reducing the stress memorization layer in the first region, and removing the stress memorization layer. The same stress memorization layer is not reduced in a region having an NMOS device. The same stress memorization layer may not be reduced in a region including a second PMOS device.