integrated power semiconductor devices having improved high frequency switching performance , improved edge termination characteristics and reduced on - state resistance include gd - umosfet unit cells with upper trench - based gate electrodes and lower trench - based source electrodes . the use of the trench - based source electrode instead of a larger gate electrode reduces the gate - to - drain capacitance of the umosfet and improves switching speed by reducing the amount of gate charging and discharging current that is needed during high frequency operation .