A novel double-density hemi-cylindrical (HC) structure 3-D NAND Flash architecture was demonstrated (Lue et al. , 2019). HC 3-D NAND squeezes the gate-all-around (GAA) hole in one direction, followed by a slit cut to split the GAA device to produce twin cells, thus creating >2.5 times of memory density than standard GAA 3-D NAND at the same stacking layer. It is demonstrated that the extremely scaled HC 3-D NAND shows excellent 100k endurance and large memory window >10 V. Contrary to the standard GAA 3-D NAND, HC device has special edge effect issue. For taller HC device, a "wake-up" effect (Du et al. , 2020) by an initial strong -FN erasing can introduce gate injected electrons that electrically suppress the parasitic edge and in turn "wake-up" the device to produce a larger programming window. TCAD simulation clearly shows asymmetrical <inline-formula> <tex-math notation="LaTeX">{E} </tex-math></inline-formula>-field distribution from bottom oxide field to top oxide field at Region I (HC tip) and Region II (bottom edge). Through the comprehensive investigation of HC device "wake-up" effect and strong -FN for initial reset, the variation of cell to cell operation window is minimized and aligned to extremely scaled "hero" HC devices that enjoy field enhancement effect (Hsu et al. , 2007). Our results suggest a promising path of 3-D NAND device toward aggressive dimension scaling and large memory window.