A trench-gate field effect transistor includes trenches extending into a silicon region of a first conductivity type, and a gate electrodes in each trench. Body regions of second conductivity type extend over the silicon region between adjacent trenches. Each body region forms a PN junction with the silicon region. A gate dielectric layer lines at least upper sidewalls of each trench, and insulates the gate electrode from the body region. Source regions of the first conductivity flank the trenches. A silicon-germanium region vertically extends through each source region and through a corresponding body region, and terminates within the corresponding body region before reaching the PN junction.