A semiconductor device includes a semiconductor substrate, a buried layer disposed in the semiconductor substrate; a deep well disposed in the semiconductor substrate; a first doped region disposed in the deep well, wherein the first doped region contacts the buried layer; a conductive region having the first conductivity type surrounding and being adjacent to the first doped region, wherein the conductive region has a concentration higher than the first doped region; a first heavily doped region disposed in the first doped region; a well having a second conductivity type disposed in the deep well; a second heavily doped region disposed in the well; a gate disposed on the semiconductor substrate between the first heavily doped region and the second heavily doped region; and a first trench structure and a second trench structure, wherein a depth of the second trench structure is substantially deeper than a depth of the buried layer.