Abstract: A memory die includes an alternating stack of insulating layers and electrically conductive layers, a semiconductor material layer located over the alternating stack, a dielectric spacer layer located over the semiconductor material layer, a memory opening vertically extending through the alternating stack, through the semiconductor material layer, and at least partly through the dielectric spacer layer, a memory opening fill structure located in the memory opening and including a dielectric core, a vertical semiconductor channel having a hollow portion which surrounds the dielectric core and a pillar portion which does not surround the dielectric core, and a memory film, and a source layer located over the dielectric spacer layer and contacting the pillar portion. In one embodiment, a tubular spacer laterally surrounds the pillar portion, is laterally spaced from the pillar portion by a cylindrical portion of the memory film, and contacts a cylindrical sidewall of the semiconductor material layer.