A high-breakdown-voltage semiconductor apparatus is provided, wherein when a gate capacitance of that portion of a gate electrode, under which a channel is formed, is Cg[F], a resistance in a channel length direction of that portion of the gate electrode, under which the channel is formed, is Rg [.OMEGA.], a threshold voltage, which is to be applied to the gate electrode and application of which permits flow of a drain current, is Vth [V], a voltage to be applied to the gate electrode to cut off the drain current is Voff [V], and a ratio of increase in the drain voltage per unit time at the time of cutting off the drain current is dV/dt [V/s], the following condition is satisfied: |Vth-Voff|.gtoreq.0.5CgRg(dV/dt)