Device self-heating effects (SHEs) in nonplanar Si MOS transistors such as fin field-effect transistors (FinFETs) and nanowire FETs have become a serious issue in designing well-tempered CMOS devices for future logic nodes. The device thermal contact resistances are strongly influenced by both the ambient temperature and within device lattice temperature. The ambient heat energy coupling through the thermal contact resistances will strongly impact device SHE in FinFETs due to increase in the surface-to-volume ratio of confined geometry thin Si Fin. In this paper, we report a 3-D quantum-corrected electrothermal numerical device analysis involving a coupled hydrodynamic and thermodynamic transport models for a target Si 3-Fin bulk n-FinFET. The numerical device simulations quantitatively predicted the impact of ambient and electrical contact temperatures on device short-channel effect immunity and performance. The simulation parameters are calibrated with the state-of-the-art Si FinFET measurement data from the literature. Our numerical simulation findings establish the phenomena of ambient temperature-induced device SHE on Si n-FinFETs performance for sub-14-nm technology nodes. The simulation predictions establish the fact that the thermal contact resistances and the within-chip ambient temperature (TA) have adverse effects on device lumped thermal resistance (Rth,eff) and performance metrics. Finally, we have numerically analyzed the FinFET design solutions (tapered source and drain regions) to improve the tolerance against the ambient temperature-induced SHE. © 1963-2012 IEEE.