A semiconductor device has a memory cell array having the arrangement of a plurality of cores, each of which comprises one block or a set of a plurality of blocks, each block defining a range of memory cells serving as a unit of data erase. The semiconductor device has a bank setting memory circuit configured to select an optional number of cores of the cores as a first bank and to set the remaining cores as a second bank, so as to allow a data read operation to be carried out in one of the first and second banks while a data write or erase operation is carried out in the other of the first and second banks.