A memory device is described, which includes a block of memory cells comprising a plurality of stacks of horizontal active lines such as NAND string channel lines, with a plurality of vertical slices penetrated by, and surrounding, the horizontal active lines to provide a gate-all-around structure. A memory film is disposed between the horizontal active lines in the plurality of stacks and the vertical slices in the plurality of vertical slices. A 3D, horizontal channel, gate-all-around NAND flash memory is provided. A method for manufacturing a memory involves a buttress process. The buttress process enables horizontal channel, gate-all-around structures.