A semiconductor device including a plurality of function units connected mutually by internal buses comprise operation mode output means provided in each of the function units and adapted to produce a request for a change from a mode of operation speed to another mode depending on data being processed; and power processing speed control means for controlling the clock frequency signal for each of the function units and the bus occupation time depending on the request for a change of operation mode so that the sum of the power consumption of the active ones of the function units may not exceed the maximum power consumption allocated to the semiconductor device. The semiconductor device can comprise a large number of function units without employing a package with high cooling efficiency or forced cooling.
