A method to fabricate an image sensor includes providing a semiconductor substrate having a pixel region and a periphery region, forming a light sensing element on the pixel region, and forming at least one transistor in the pixel region and at least one transistor in the periphery region. The step of forming the at least one transistor in the pixel region and periphery region includes forming a gate electrode in the pixel region and periphery region, depositing a dielectric layer over the pixel region and periphery region, partially etching the dielectric layer to form sidewall spacers on the gate electrode and leaving a portion of the dielectric layer overlying the pixel region, and forming source/drain (S/D) regions by ion implantation.