A semiconductor device includes a transistor formed in a semiconductor substrate having a main surface. The transistor includes a source region of a first conductivity type, a drain region of the first conductivity type, a channel region of a second conductivity type, a gate trench adjacent to a first sidewall of the channel region, a gate conductive material disposed in the gate trench, the gate conductive material being connected to a gate terminal, and a channel separation trench adjacent to a second sidewall of the channel region. The second sidewall faces the first sidewall via the channel region. The channel separation trench is filled with an insulating separation trench filling consisting of an insulating material in direct contact with the channel region. The source region and the drain region are disposed along a first direction. The first direction is parallel to the main surface.