A memory device which can be configured as a 3D NAND flash memory, includes a plurality of stacks of conductive strips, including even stacks and odd stacks having sidewalls. Some of the conductive strips in the stacks are configured as word lines. Data storage structures are disposed on the sidewalls of the even and odd stacks. Active pillars between corresponding even and odd stacks of conductive strips include even and odd semiconductor films having outside surfaces and inside surfaces, the outside surfaces disposed on the data storage structures on the sidewalls of the corresponding even and odd stacks in the plurality of stacks forming a 3D array of memory cells, the inside surfaces are separated by an insulating structure that can include a gap. The semiconductor films can be thin-films.