A semiconductor device includes a trench extending into a drift zone of a semiconductor body from a first surface. The semiconductor device further includes a gate electrode in the trench and a body region adjoining a sidewall of the trench. The semiconductor device further includes a dielectric structure in the trench. The dielectric structure includes a high-k dielectric in a lower part of the trench. The high-k dielectric includes a dielectric constant higher than that of SiO2. An extension of the high-k dielectric in a vertical direction perpendicular to the first surface is limited between a bottom side of the trench and a level where a bottom side of the body region adjoins the sidewall of the trench.