The high-voltage transistor device comprises a semiconductor substrate (1) with a source region (2) of a first type of electrical conductivity, a body region (3) including a channel region (4) of a second type of electrical conductivity opposite to the first type of conductivity, a drift region (5) of the first type of conductivity, and a drain region (6) of the first type of conductivity extending longitudinally in striplike fashion from the channel region (4) to the drain region (6) and laterally confined by isolation regions (9). The drift region (5) comprises a doping of the first type of conductivity and includes an additional region (8) with a net doping of the second type of conductivity to adjust the electrical properties of the drift region (5). The drift region depth and the additional region depth do not exceed the maximal depth (17) of the isolation regions (9).