It is demonstrated that the strained-Si can enhance the channel stress with the contact etching stop layer (CESL) stressor. In addition to CESL, this article also includes ONO spacer and investigates the impact of ONO spacer thickness on the channel stress. It is found that the channel stress increases when the nitride thickness of the ONO spacer increases. On the other hand, the stress distribution is simulated and analyzed for the devices with or without CESL stressor. Generally speaking, based on the simulation results, the channel stress of MOSFET devices increases when the nitride stressor of ONO spacer and/or CESL increases.