A semiconductor device capable of high-voltage operation includes a semiconductor substrate having a first conductivity type. A first well doped region is formed in the semiconductor substrate, having a second conductivity type that is the opposite of the first conductivity type. A first doped region and a second doped region are formed on the first well doped region, having the second conductivity type. A first gate structure is formed over the first well doped region and adjacent to the first doped region. A second gate structure overlaps the first gate structure and the first well doped region. A third gate structure is formed beside the second gate structure and close to the second doped region. The top surface of the first well doped region between the second gate structure and the third gate structure avoids having any gate structure and silicide formed thereon.