A method for forming a field-effect semiconductor device includes: providing a wafer having a main surface and a first semiconductor layer of a first conductivity type; forming at least two trenches from the main surface partly into the first semiconductor layer so that each of the at least two trenches includes, in a vertical cross-section substantially orthogonal to the main surface, a side wall and a bottom wall, and that a semiconductor mesa is formed between the side walls of the at least two trenches; forming at least two second semiconductor regions of a second conductivity type in the first semiconductor layer so that the bottom wall of each of the at least two trenches adjoins one of the at least two second semiconductor regions; and forming a rectifying junction at the side wall of at least one of the at least two trenches.