A high-voltage semiconductor device has a main high-voltage switch device and a current-sense device for mirroring the current through the main high-voltage switch device. The main high-voltage switch device has a plurality of switch cells arranged to form a first array on a semiconductor substrate. Each switch cell has a first cell width. The current-sense device has a plurality of sense cells arranged to form a second array on the semiconductor substrate. Each sense cell has a second cell width larger than the first cell width. The switch cells and the sense cells share a common gate electrode and a common drain electrode.