A semiconductor device according to an embodiments controls a gate voltage to be applied to a gate electrode of a junction field effect transistor including a source electrode, a drain electrode, and the gate electrode, the transistor having a first threshold voltage at which the transistor is turned on, and a second threshold at which conductivity modulation occurs in the transistor so as to make the gate voltage equal to or higher than the second threshold voltage when a forward current in a direction from the drain electrode toward the source electrode flows, and so as to make the time variation in gate voltage have a point from which the rate of the time variation starts decreasing at a voltage between the second threshold voltage and the first threshold voltage when the forward current to be shut down.