A semiconductor device comprises a transistor in a semiconductor body having a first main surface and a second main surface, the first main surface being opposite to the second main surface. The transistor comprises a source region at the first main surface, a drain region, a body region, a drift zone, and a gate electrode at the body region. The body region and the drift zone are disposed along a first direction between the source region and the drain region, the first direction being parallel to the first main surface. The gate electrode is disposed in trenches extending in the first direction. The transistor further comprises an insulating layer adjacent to the second main surface of the body region. The source region vertically extends to the second main surface.