A highly reliable semiconductor device in which a shift in threshold voltage of a transistor due to deterioration can be inhibited is provided. A pulse output circuit includes a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, and a sixth transistor. A clock signal is supplied to a drain of the first transistor. A first power supply potential is applied to a source of the second transistor, and a drain of the second transistor is connected to the drain of the first transistor. A second power supply potential is applied to a drain of the third transistor. The first power supply potential is applied to a source of the fourth transistor, and a drain of the fourth transistor is connected to the drain of the third transistor. The first power supply potential is applied to a source of the fifth transistor, and a drain of the fifth transistor is connected to a gate of the third transistor. One of a source and a drain of the sixth transistor is connected to the drain of the first transistor, and the other of the source and the drain of the sixth transistor is connected to the gate of the third transistor. The first transistor and the third transistor include back gates connected to each other. The first to sixth transistors have the same conductivity type.