Patent ID: 6917071

Claim:
A nonvolatile semiconductor memory device comprising: a plurality of bit lines arranged in a semiconductor substrate; a plurality of word lines above said semiconductor substrate arranged to intersect the bit lines; and a plurality of said semiconductor devices which are disposed at respective intersections of said bit lines and said word lines, each of said semiconductor devices includes: a first gate insulating film on a semiconductor substrate, an isolating gate electrode on said first gate insulating film, an isolating insulating film on the top surface of said isolating gate electrode and a side surface of said isolating gate electrode, a floating gate on said isolating insulating film, a second gate insulating film on said floating gate, a control gate on said second gate insulating film; and a source region and a drain region in said semiconductor substrate on opposite sides of said floating gate; wherein said floating gate comprises a first floating gate portion which is on said first gate insulating film and is adjacent to said isolating gate electrode through a part of said isolating insulating film on said side surface of said isolating gate electrode and a second floating gate portion which is on said first floating gate portion and on a part of said isolating insulating film on said top surface of said isolating gate electrode, wherein said plurality of bit lines includes said drain regions and said plurality of word lines includes said control gate, further comprising: an X decoder which selects one of said word lines, a Y decoder which selects one of said buried bit lines; and a sub Y decoder which selects one of said isolating gates, wherein said X decoder supplies a first individual voltage to one of said word lines which a selected semiconductor device belongs to, said Y decoder supplies a second individual voltage to one of said buried bit lines which is adjacent to said selected semiconductor device, said sub Y decoder selects none of said isolating gates at a writing time.