The present disclosure provides a semiconductor device. The semiconductor device includes a first doped region and a second doped region both formed in a substrate. The first and second doped regions are oppositely doped. The semiconductor device includes a first gate formed over the substrate. The first gate overlies a portion of the first doped region and a portion of the second doped region. The semiconductor device includes a second gate formed over the substrate. The second gate overlies a different portion of the second doped region. The semiconductor device includes a first voltage source that provides a first voltage to the second gate. The semiconductor device includes a second voltage source that provides a second voltage to the second doped region. The first and second voltages are different from each other.