Manufacturing method of high-voltage semiconductor device with increased breakdown voltage

A method for manufacturing a high voltage semiconductor device, comprising:

• providing a semiconductor substrate having a first conductivity type, wherein the semiconductor substrate has an active area;
• forming at least one first isolation structure and at least one second isolation structure in the active area of the semiconductor substrate;
• forming a gate structure on the active area of the semiconductor substrate and at a side of the at least one first isolation structure in a top view of the high voltage semiconductor device, wherein the gate structure extends along a first direction, and an end of the at least one second isolation structure is disposed between the at least one first isolation structure and the gate structure in a second direction perpendicular to the first direction;
• and
• forming at least one first drift region in the active area of the semiconductor substrate at a side of the gate structure in the top view, and the at least one first drift region having a second conductivity type complementary to the first conductivity type, wherein a bottom of the at least one first isolation structure and a bottom of the at least one second isolation structure are deeper than a bottom of the at least one first drift region.