A temperature detector sets the level of a temperature detecting signal to a level indicating a high temperature state, detecting that the chip temperature is higher than a first boundary temperature. The temperature detector sets the level of thereof to a level indicating a low temperature state, detecting that the chip temperature is lower than a second boundary temperature. A control circuit changes its operating state according to the level of the temperature detecting signal. This prevents the operating state of the control circuit from frequently switched even when the chip temperature fluctuates around the boundary temperatures, and accordingly reduces current consumption of the control circuit due to the switching operation. Further, the first and second boundary temperatures set a buffer zone, so that the temperature detector does not detect power supply noises as temperature variation. This can prevent malfunction of the temperature detector and the semiconductor integrated circuit.