A novel semiconductor device or a novel display system is provided. A signal generation portion monitors display conditions and controls the potentials output from a power supply circuit, in accordance with the display conditions. Specifically, a controller changes the parameter stored in a memory device when display conditions change. Then, the power supply circuit generates the potentials with the use of the changed parameter. Accordingly, the voltage applied to a light-emitting element can be controlled in accordance with the display conditions, which reduces the power consumption in a display portion.