A semiconductor device is manufactured by forming a gate electrode adjacent to a body region in a semiconductor substrate, forming a field plate trench in a main surface of the substrate, the field plate trench having an extension length in a first direction parallel to the main surface, and forming a field electrode and a field dielectric layer in the field plate trench so that the field electrode is insulated from an adjacent drift zone by the field dielectric layer. The extension length of the field plate trench in the first direction is less than double an extension length of the field electrode in a second direction that is perpendicular to the first direction and is parallel to the main surface. The extension length in the first direction is more than half the extension length in the second direction.