A high voltage (HV) semiconductor device is provided, comprising a substrate, a first well having a first conductive type and extending down from a surface of the substrate; a plurality of active devices respectively formed on the substrate, and the adjacent active devices electrically separated from each other by an insulation. One of the active devices comprises a diffusion region doped with impurity of the first conductive type and extending down from a surface of the first well, a ring gate formed in the diffusion region, and a light doping region having a second conductive type and extending down from a surface of the diffusion region. The light doping region is offset from an edge of the insulation.