Method of manufacturing trench gate semiconductor devices

The manufacture of a vertical power transistor trench-gate semiconductor device in which the source regions (13) are self-aligned to the trench-gate structures (20,17,11) including the steps of forming a mask (61) on a surface (10a) of a semiconductor body (10), using the mask (61) to form the trench-gate structures (20,17,11), then using the mask (61) to form U-shaped section layers (62A, 62B) of insulating material whose base portion (62B) provides a gate insulating layer on the gate material (11), then removing the mask (61) and forming spacers (64) against well-defined steps provided by the upright portions (62A) of the U-shaped section layers, then using the spacers (64) to form the source regions (13).