A semiconductor device includes a plurality of semiconductor chips and a memory device. The semiconductor chips are provided in a package. Each of the semiconductor chips includes a memory cell array having memory cells which stores data, an output buffer which outputs data read from the memory cell array to an exterior of the semiconductor chip and a control circuit which controls driving power of the output buffer. The memory device stores the number of semiconductor chips provided in the package. The control circuit controls the driving power according to the number of semiconductor chips stored in the memory device.