In this paper, we examine the effects of process variation effect (PVE) and intrinsic parameter fluctuation (IPF) including work function fluctuation (WKF) and random dopant fluctuation (RDF) on characteristic variability of stacked gate-all-around silicon nanosheet complementary field-effect transistors (GAA Si NS CFETs). Among the examined factors in PVE, the channel thickness (TNS), channel width (WNS), and gate length (LG) are the most sensitive factors. The impacts of IPF are suppressed by a larger effective area of gate control. The PVEs on both N-/P-FETs of the GAA Si NS CFETs led to large off-state current (Ioff) fluctuations of 80% and 270%, respectively. Device characteristics are highly sensitive to TNS and WNS. P-type device even suffers serious Ioff fluctuation because its bottom channel is a kind of FinFET type.