The source 38 and the drain 39 have the second conductivity type. The source 38 and the drain 39 are formed below the top surface 31a and in contact with the top surface 31a in the vertical direction within the device region 33a. The source 38 and the drain 39 are located below and outside two sides of the gate 37 respectively, wherein the source 38 is located in the body region 36, and the drain 39 is located in the first high voltage well 32, at a location near the right side of the gate 37 (i.e., the side that is away from the body region 36) . An inversion region 36a is formed in the body region 36 between the source 38 and the first high voltage well 32 in a channel direction (indicated by a dashed arrow), and is in contact with the top surface 31a, to serve as an inversion current channel in an ON operation of the high voltage device 300. A drift region 32a is formed in the first high voltage well 32 between the drain 39 and the body region 36 in the channel direction, and is in contact with the top surface 31a, to serve as a drift current channel in the ON operation of the high voltage device 300. The deep well column 35 is located between the drain 39 and the left boundary of the conductive layer 372 (i.e., the boundary of the conductive layer 372 which is near the source 38) in the channel direction, i.e., between the vertical lines AA′ and BB′ shown in the figure.