A semiconductor device of an embodiment is provided with a normally-off transistor having a first source connected to a source terminal, a first drain, and a first gate connected to a gate terminal and a normally-on transistor having a second source connected to the first drain, a second drain connected to a drain terminal, and a second gate connected to the source terminal. A withstand voltage between the first source and the first drain when the normally-off transistor is turned off is lower than a withstand voltage between the second source and the second gate of the normally-on transistor.