Transistor device having a field plate

A transistor device includes a semiconductor substrate having a first major surface, a cell field and an edge termination region laterally surrounding the cell field. The cell field includes: elongate active trenches that extend from the first major surface into the semiconductor substrate, a field plate and a gate electrode being positioned in each elongate active trench, the gate electrode being arranged above and electrically insulated from the field plate; and elongate mesas, each elongate mesa being formed between neighbouring elongate active trenches, the elongate mesas comprising a drift region, a body region on the drift region and a source region on the body region.