High voltage semiconductor device and manufacturing method thereof

A high voltage semiconductor device, comprising:

• a semiconductor substrate;
• a gate structure disposed on the semiconductor substrate;
• a first doped well disposed in the semiconductor substrate, wherein the first doped well comprises a first conductivity type dopant;
• a second doped well disposed in the semiconductor substrate, wherein the second doped well comprises a second conductivity type dopant, and at least a part of the first doped well and at least a part of the second doped well are located at two opposite sides of the gate structure in a horizontal direction respectively;
• a mixed doped well disposed in the semiconductor substrate, wherein the mixed doped well is located between the first doped well and the second doped well in the horizontal direction, and the mixed doped well comprises a mixed dopant, wherein a part of the mixed dopant is identical to the first conductivity type dopant, and another part of the mixed dopant is identical to the second conductivity type dopant;
• a drain doped region disposed in the first doped well;
• and
• a source doped region disposed in the second doped well, wherein the drain doped region and the source doped region are located at the two opposite sides of the gate structure in the horizontal direction respectively, and a ratio of a length of the mixed doped well in the horizontal direction to a distance between the source doped region and the mixed doped well in the horizontal direction ranges from 0.8 to 1.