There is disclosed a semiconductor integrated circuit device including a memory cell array having a plurality of blocks, a first non-volatile semiconductor memory cell which is arranged in the memory cell array and has an electric charge storage layer, and a second non-volatile semiconductor memory cell which is arranged in the memory cell array to be adjacent to the first non-volatile semiconductor memory cell and has an electric charge storage layer. Regular data writing is performed with respect to the second non-volatile semiconductor memory cell after regular data writing is carried out with respect to the first non-volatile semiconductor memory cell. Additional data writing is performed with respect to the first non-volatile semiconductor memory cell after regular data writing is carried out with respect to the second non-volatile semiconductor memory cell.