High voltage semiconductor device

A high voltage semiconductor device, comprising:

• a semiconductor substrate;
• a first deep well region disposed in the semiconductor substrate;
• a second deep well region disposed in the semiconductor substrate and located above the first deep well region in a vertical direction, wherein a conductivity type of the second deep well region is complementary to a conductivity type of the first deep well region;
• a first well region disposed in the semiconductor substrate and located above the first deep well region in the vertical direction;
• a second well region disposed in semiconductor substrate and located above the second deep well region in the vertical direction, wherein a conductivity type of the second well region is complementary to a conductivity type of the first well region, and the conductivity type of the second well region is complementary to the conductivity type of the second deep well region;
• a gate structure disposed on the semiconductor substrate, wherein a part of the first well region and a part of the second well region are located at two opposite sides of the gate structure in a horizontal direction, respectively;
• an isolation structure disposed in the first well region;
• and
• a third well region disposed in the semiconductor substrate and located between the isolation structure and the first deep well region in the vertical direction, wherein a part of the first well region is sandwiched between the third well region and the second deep well region in the horizontal direction.