A method of forming a memory device, comprising: forming a plurality of separated first trenches into a surface of a semiconductor substrate, wherein the first trenches are parallel to each other and extend in a first direction and define active regions of the substrate between the first trenches; filling the first trenches with insulation material; forming a first insulation layer on the surface of the substrate in each of the active regions; forming a first conductive layer on the first insulation layer in each of the active regions; forming a second insulation layer on the first conductive layer in each of the active regions; forming a second conductive layer on the second insulation layer in each of the active regions; forming a third insulation layer on the second conductive layer in each of the active regions; forming a plurality of separated second trenches through the third insulation layer, wherein the second trenches are parallel to each other and extend in a second direction perpendicular to the first direction; extending the second trenches through the second conductive layer and the second insulation layer and into the first conductive layer; after said step of extending the second trenches, forming spacers of insulation material along side walls of the second trenches; after said step of forming the spacers of insulation material, extending the second trenches through the first conductive layer, leaving side portions of the first conductive layer exposed and leaving the first insulation layer on the surface of the substrate at the bottom of the second trenches exposed; forming a fourth insulation layer on the exposed first insulation layer at the bottom of the second trenches, wherein said fourth insulation layer extends along the exposed portions of the first conductive layer and along the spacers of insulation material; filling the second trenches with conductive material, wherein the conductive material is insulated from the first conductive layer only by the fourth insulation layer, is insulated from the substrate surface by the first insulation layer and the fourth insulation layer and is insulated from the second conductive layer by the spacer of insulation material and the fourth insulation layer; after said step of filling the second trenches with conductive material, forming a plurality of third trenches through the third insulation layer, wherein the third trenches are parallel to each other and extend in the second direction such that the second and third trenches (32, 38) alternate each other; extending the third trenches through the second conductive layer, the second insulation layer, and the first conductive layer; performing an implantation to form drain regions (12A, 12B) in the substrate under the third trenches. forming a plurality of separated first trenches into a surface of a semiconductor substrate, wherein the first trenches are parallel to each other and extend in a first direction and define active regions of the substrate between the first trenches; filling the first trenches with insulation material; forming a first insulation layer on the surface of the substrate in each of the active regions; forming a first conductive layer on the first insulation layer in each of the active regions; forming a second insulation layer on the first conductive layer in each of the active regions; forming a second conductive layer on the second insulation layer in each of the active regions; forming a third insulation layer on the second conductive layer in each of the active regions; forming a plurality of separated second trenches through the third insulation layer, wherein the second trenches are parallel to each other and extend in a second direction perpendicular to the first direction; extending the second trenches through the second conductive layer and the second insulation layer and into the first conductive layer; after said step of extending the second trenches, forming spacers of insulation material along side walls of the second trenches; after said step of forming the spacers of insulation material, extending the second trenches through the first conductive layer, leaving side portions of the first conductive layer exposed and leaving the first insulation layer on the surface of the substrate at the bottom of the second trenches exposed; forming a fourth insulation layer on the exposed first insulation layer at the bottom of the second trenches, wherein said fourth insulation layer extends along the exposed portions of the first conductive layer and along the spacers of insulation material; filling the second trenches with conductive material, wherein the conductive material is insulated from the first conductive layer only by the fourth insulation layer, is insulated from the substrate surface by the first insulation layer and the fourth insulation layer and is insulated from the second conductive layer by the spacer of insulation material and the fourth insulation layer; after said step of filling the second trenches with conductive material, forming a plurality of third trenches through the third insulation layer, wherein the third trenches are parallel to each other and extend in the second direction such that the second and third trenches (32, 38) alternate each other; extending the third trenches through the second conductive layer, the second insulation layer, and the first conductive layer; performing an implantation to form drain regions (12A, 12B) in the substrate under the third trenches.