A nonvolatile semiconductor memory device has a high read output and is not affected by a noise of adjacent bit lines. The memory device is capable of performing high speed read operations. Each bit of a memory as formed by a plurality of memory cells. The memory cells each have the same structure as the structure of a memory cell of the main memory. During a read operation, the bit line is selected and proximate bit lines proximate to the selected bit line are not selected. The nonvolatile semiconductor memory device is formed together with the main memory on one chip by the same process.