US Patent 7433230 Nonvolatile semiconductor memory device having assist gate

In this AG-AND type flash memory, a layered bit line configuration where a memory array is divided into a plurality of sub blocks, new main bit lines are allocated so as to correspond to each sub block, and a main bit line is selectively connected to a global bit line in an upper layer via a switch is adopted, so that charge sharing write-in is carried out between two main bit lines. Accordingly, write-in of data into the flash memory can be carried out with low power consumption, and the threshold voltage can be controlled with precision.