Abstract: A nonvolatile semiconductor memory device disclosed herein includes: a reference cell held in an ON-state; a reference cell held in an OFF-state; a driving transistor which is turned ON by a signal for reading out data from a memory cell, to supply a current to the memory cell; driving transistors which have a same construction and characteristics as the driving transistor and also which are turned ON by that signal to supply a current to the reference cells; and a sense-amplifier which has a first input terminal supplied with an output voltage of the driving transistor and a second input terminal supplied with an average (VRon+VRoff)/2 of output voltages VRon and VRoff of the driving transistors respectively.

Abstract: In a non-volatile semiconductor storage, at the time of a data writing, the size of the data to be written is compared with the size of an erase block and/or the size of a writable storage unit in the erase block. The data having the size corresponding to the size of the erase block is written into a writable erase block, and the data having the size smaller than the size of the erase block is written into the writable storage unit(s), so that a storing area optimum to the size of the data to be written is allocated.

Abstract: It is an object of the invention to provide an EEPROM, in which the third positive potential for erase verify is supplied from a negative potential generating circuit for supplying a negative or ground potential to a word line. The EEPROM is composed of a P potential supply circuit for respectively supplying a potential to sources of P channel transistors in invertors, which are respectively connected with word lines, a N potential supply circuit for respectively supplying a potential to sources of N channel transistors in the invertors, a read/write decision circuit for deciding whether the EEPROM operates in a read or write mode, and an erase decision circuit for deciding whether the EEPROM operates in an erase mode or not.

Abstract: In a semiconductor memory device comprising a plurality of memory arrays, the memory array is given a predetermined potential from a terminal via a reference line. Further, a plurality of source switches are connected to the memory arrays and the reference line. The source switches selectively transfer the predetermined potential to each of the memory arrays. In this case, each of the source switches includes a transistor having an electrical ability which is determined by a length of the reference line between each source switch and the terminal.When the transistor is formed by a MOS transistor, the above electrical ability is specified by the ON resistance of the MOS transistor. The MOS transistors are designed so that the ON resistance becomes lower as the length of the reference line between the source switch and the terminal becomes longer.