Present disclosure provides a semiconductor structure, including a semiconductor substrate having a top surface, a first well region of a first conductivity type in the semiconductor substrate, a second well region of a second conductivity type in the semiconductor substrate, laterally surrounding the first well region, and an isolation region in the first well region and the second well region in proximity to the top surface. The first well region includes a first lighter doped region in proximity to the top surface, and a heavier doped region under the first lighter doped region. Present disclosure also provides a method for manufacturing the semiconductor structure described herein.