A method for controlling power supply in a semiconductor device including a CPU and a PLD which can hold data even in an off state is provided. The semiconductor device includes a processor, a programmable logic device, and a state control circuit. The programmable logic device includes a first nonvolatile memory circuit and has a function of holding data obtained by arithmetic processing of the programmable logic device when it is turned off. The state control circuit obtains data on the amount of a task performed by the programmable logic device in accordance with an operation of the processor. The programmable logic device detects the state of progress of the task and outputs a signal to the state control circuit. The state control circuit monitors the amount of the task and the state of progress of the task and turns off the programmable logic device when the task is completed.