A semiconductor device includes an electrode arranged on a main surface of a semiconductor body and an insulating structure insulating the electrode from the semiconductor body. The insulating structure includes in a vertical cross-section a gate dielectric portion forming a first horizontal interface at least with a drift region of the device and having a first maximum vertical extension between the first horizontal interface and the electrode, and a field dielectric portion forming with the drift region second, third and fourth horizontal interfaces. The second through fourth horizontal interfaces are arranged below the main surface. The third horizontal interface is arranged between the second and fourth horizontal interfaces. A second maximum vertical extension is larger than the first maximum vertical extension and a third maximum vertical extension is larger than the second maximum vertical extension. The electrode only partially overlaps the third horizontal interface.