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This paper presents vertical-Si-nanowire (SiNW) gate-all-around nonvolatile memory (NVM) devices of two different kinds: junction based and junctionless (JL). Si nanocrystals (SiNCs) and silicon nitride (SiN) are used as trap layers. The devices are fabricated using complementary-metal-oxide-semiconductor-compatible top-down process technology and compared on the bases of improved performance and reduced process complexity. The junction-based 50-nm vertical-SiNW memory device with a SiNC trap layer shows significant performance improvements on program/erase (P/E) speed and windows (3.5 V in 1-ms P/E at +15/-16 V) over a memory cell with a SiN trap layer (1.3 V in 1-ms P/E at +15/-16 V). On the other hand, the JL device with a SiN trap layer, realized on a highly scaled SiNW channel (down to 20 nm), is found to have comparable memory characteristics (3.2 V in 1-ms P/E at +15/-16 V) to a corresponding 20-nm SiNW junction-based cell (2.7 V in 1-ms P/E at +15/-16 V). Despite of that, the absence of junctions reduces process complexity and makes a vertical SiNW a suitable platform for multilevel stacked ultrahigh density memory applications.