The source 28 and the drain 29 have the second conductivity type. The source 28 and the drain 29 are formed below the top surface 21a and in contact with the top surface 21a in the vertical direction within the device region 23a. The source 28 and the drain 29 are located below and outside two sides of the gate 27 respectively, wherein the source 28 is located in the body region 26, and the drain 29 is located in the first high voltage well 22, at a location near the right side of the gate 27 (i.e., the side that is away from the body region 26) . An inversion region 26a is formed in the body region 26 between the source 28 and the first high voltage well 22 in a channel direction (indicated by a dashed arrow), and is in contact with the top surface 21a, to serve as an inversion current channel in an ON operation of the high voltage device 200. A drift region 22a is formed in the first high voltage well 22 between the drain 29 and the body region 26 in the channel direction, and is in contact with the top surface 21a, to serve as a drift current channel in the ON operation of the high voltage device 200. The deep well column 25 is located between the drain 29 and the left boundary of the conductive layer 272 (i.e., the boundary of the conductive layer 272 which is near the source 28) in the channel direction, i.e., between the vertical lines AA′ and BB′ shown in the figure.