Patent ID: 7847342

Claim:
A non-volatile semiconductor storage device comprising a plurality of memory strings with a plurality of electrically rewritable memory cells connected in series, each of the memory strings comprising: a first columnar semiconductor layer extending in a direction perpendicular to a substrate and having a first hollow extending downward from its upper end; a first insulation layer formed in contact with an outer wall of the first columnar semiconductor layer; a second insulation layer formed on an inner wall of the first columnar semiconductor layer so as to leave the first hollow, the inner wall facing the first hollow; and a plurality of first conductive layers formed to sandwich the first insulation layer with the first columnar semiconductor layer and functioning as control electrodes of the memory cells; and a third insulation layer formed in contact with the second insulation layer so as to fill up the first hollow, one or more voids being formed in the third insulation layer.