Nonvolatile semiconductor memory device for storing multivalued data

A multivalued memory has data of state "0", state "1", state "2", and state "3" whose threshold voltages increase in that order. In a first-page write operation, a memory cell whose data is in state "0" is brought into state "1". In a second-page write operation, a memory cell whose data is in state "0" is brought into state "3" and a memory cell whose data is in state "1" is brought into state "2". As a result, in reading the data, the data on the first page can be read in two read operations. Furthermore, the operation of writing the data onto the second page can be made faster, because a high initial write voltage can be used.