In a semiconductor device having a large-scale arithmetic circuit, when there is delay in clock signals, a malfunction occurs in a circuit. In particular, in an environment where supply voltage varies as in a wireless chip, it is very difficult to precisely estimate delays in clock signals in designing. Further, in order to keep supply voltage stable, a large-scale power supply circuit is required, which increases the area of a chip, and the cost thereof. A semiconductor device provided with a power control circuit and a clock generation circuit is used to detect variation in supply voltage using the power control circuit and changing frequency and duty ratio of a clock circuit using the clock generation circuit, thereby operating an arithmetic circuit stably. A high performance semiconductor device provided with such a large-scale arithmetic circuit can be provided at low cost.