Abstract: A trench-gate semiconductor device, for example a MOSFET or IGBT, of compact geometry is manufactured with self-aligned masking techniques in a simple process with good reproducibility. The source region (13) of the device is formed by introducing dopant (63) into an area of the body region (15) via a mask window (51a), diffusing the dopant to form a surface region (13b) that extends laterally below the mask (51) at a distance (d) beyond the masking edge (51b) of the window (51a), and then etching the body (10) at the window (51a) to form a trench (20) for the trench-gate (11) with a lateral extent (y) that is determined by the etching of the body (10) at the masking edge (51b) of the window (51a). A portion of the surface region (13b) is left to provide the source region (13) adjacent to the trench (20).