A semiconductor device includes a transistor in a semiconductor substrate having a main surface. The transistor includes a source region, a drain region, a body region, and a gate electrode structure adjacent to the body region. The source region and the drain region are disposed along a first direction, the first direction being parallel to the main surface. The body region is disposed between the source region and the drain region. The body region includes an upper body region at the main surface and a lower body region remote from the main surface. A first width of the lower body region is smaller than a second width of the upper body region. The first width and the second width are measured in a direction perpendicular to the first direction.