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This paper investigates the sensitivity of gate-all-around (GAA) nanowire (NW) to process variations compared with multigate devices using analytical solutions of Poisson's equation verified with device simulation. GAA NW and multigate devices with both heavily doped and lightly doped channels have been examined regarding their immunity to process-induced variations and dopant number fluctuation. Our study indicates that the lightly doped GAA NW has the smallest threshold voltage (V th) dispersion caused by process variations and dopant number fluctuation. Specifically, the GAA NW shows better immunity to channel thickness variation than multigate devices because of its inherently superior surrounding gate structure. For heavily doped devices, dopant number fluctuation may become the dominant factor in the determination of overall V th variation. The V th dispersion of GAA NW may therefore be larger than that of multigate MOSFETs because of its larger surface-to-volume ratio.