A high-voltage semiconductor device is disclosed. The HV semiconductor device includes: a substrate; a well of first conductive type disposed in the substrate; a first doping region of second conductive type disposed in the p-well; a first isolation structure disposed in the well of first conductive type and surrounding the first doping region of second conductive type; and a first drift ring of second conductive type disposed between the first doping region of second conductive type and the first isolation structure.