A highly reliable semiconductor device is provided. A semiconductor device includes a shift register including a pulse output circuit formed using transistors having the same conductivity type, or the like. A transistor including a back gate is used as a transistor in which a potential difference between a source and a drain is not generated and positive stress is applied to a gate in a non-selection period of the pulse output circuit. In the non-selection period, stress applied to the transistors is reduced by interchanging the potentials of the gates and those of the back gates.