Abstract: Methods of forming semiconductor switching devices having trench-gate electrodes include the steps of implanting base region dopants of second conductivity type into a semiconductor substrate to define a preliminary base region therein. A step is then performed to form a trench having sidewalls which extend through the preliminary base region. A sacrificial insulating layer is then formed on the sidewalls of the trench while the implanted base region dopants are simultaneously diffused into the region of first conductivity type. The sacrificial insulating layer is then removed. Next, a gate electrode insulating layer is formed on the sidewalls and on a bottom of the trench. A gate electrode is then formed on the gate electrode insulating layer. Dopants of first conductivity type are then implanted into the semiconductor substrate to define a preliminary source region, which forms a P-N junction with the implanted base region dopants, and into the gate electrode to improve the conductivity thereof.