A semiconductor device includes a memory cell array including a plurality of cores, each of said cores including one block or a plurality of blocks. The semiconductor device further includes a first power supply line which is provided commonly for said plurality of cores and which provides a data reading power supply potential; a second power supply line which is provided commonly for said plurality of cores and which provides a data writing or erasing power supple potential; and a power supply line switching circuit which is provided for each of said plurality of cores and which selectively connects a corresponding one of said plurality of cores to said first power supply line or said second power supply line in accordance with whether said corresponding one of said plurality of cores is in a data read mode or a data write or erase mode.