High voltage-resistant semiconductor devices adapted to control threshold voltage by utilizing threshold voltage variation caused by plasma damage resulting from the formation of multilayer wiring, and a manufacturing method thereof. Exemplary high voltage-resistant semiconductor devices include a plurality of MOS transistors having gate insulating films not less than about 350 Å in thickness on a silicon substrate, and the MOS transistors have different area ratios between gate electrode-gate insulating film contact areas and total opening areas of contacts formed on the gate electrodes.