To suppress a decrease in photosensitivity of a photoelectric conversion element provided in a semiconductor device by reducing the parasitic resistance of an amplifier circuit. In addition, the amplifier circuit which amplifies the output current of the photoelectric conversion element is operated stably. A semiconductor device includes a photoelectric conversion element, a current mirror circuit having at least two thin film transistors, a high-potential power supply electrically connected to each of the thin film transistors, and a low-potential power supply electrically connected to each of the thin film transistors. When a reference thin film transistor is an n-type, the reference thin film transistor is placed closer to the low-potential power supply than an output thin film transistor is. When a reference thin film transistor is a p-type, the reference thin film transistor is placed closer to the high-potential power supply than an output thin film transistor is.