In this article, the effects of non-ideal cross-sectional shapes of stacked nanosheet FET (NSFET) and nanosheet FET with inter-bridge channel (TreeFET) are studied through calibrated 3D TCAD simulations. The impact of non-ideal cross-sectional shapes on the electrical characteristics due to insufficient/excessive etch processes are investigated in terms of inner spacer (IS), nanosheet (NS) channel, and inter-bridge (IB) channel. Simulation results show that the geometry and material of the IS have significant effects on the performance of the NSFET. Compared with the rectangular inner spacer (RIS), the low-k crescent inner spacer (CIS) enhances the gate control capability while the high-k CIS degrades the drain-induced barrier lowering (DIBL) and reduces the gate capacitance (Cgg). The tapered NS channel improves short-channel effects (SCEs), but sacrifices the driving current. For the TreeFET, considering the fin angle and concave arc, the IB channel can degrade the gate control capability, and SCEs degradation is severe compared to the ideal structure. Therefore, the non-ideal cross-sectional shapes have a significant impact on NSFET-based structure. This research provides development guidelines for process and structure optimization in advanced transistor technology nodes.