The semiconductor structure includes a substrate, a deep well, a first doped region, a source/drain region, and a first heavily doped region. The substrate has a first conductivity type. The deep well has a second conductivity type disposed on the substrate. The first doped region has the first conductivity type disposed on the deep well. The source/drain region has the second conductivity type disposed on the first doped region. The first heavily doped region has the second conductivity type disposed in a first top region of the source/drain region, in which the first conductivity type is opposite to the second conductivity type.