To provide a semiconductor device that reduces power consumption and prevents an increased circuit area by constituting a standby circuit with fewer elements.

The standby circuit in the semiconductor device comprises only one transistor, and switching a voltage supplied to the transistor controls an output current of the semiconductor device. As a result, the output current of the semiconductor device in a standby state can be substantially zero to reduce power consumption. The use of an oxide semiconductor for a semiconductor layer of the transistor can minimize a leakage current.