A semiconductor device in which a transistor can supply an accurate current to a load (EL pixel and signal line) without being influenced by variations is provided.A voltage at each terminal of a transistor is adjusted by a feedback circuit using an amplifier circuit. A current Idata is input from a current source circuit to the transistor, and a gate-source voltage is set by the feedback circuit so that the transistor can flow the current Idata. The feedback circuit controls the transistor to operate in a saturation region. Thus, a gate voltage required for flowing the current Idata is set. With the use of the set transistor, a current can be supplied to a load (EL pixel and signal line) with accuracy. Note that a desired gate voltage can be set quickly since the amplifier circuit is utilized.