We have investigated the impact of surface orientation on the V th variability of Si- and Ge-FinFET using both the analytical solution of Schrödinger equation and atomistic simulation. Our study indicates that, for ultra-scaled FinFET, the importance of tch variation increases due to the quantumconfinement effect. The Si-(100) and Ge-(111) surface show lower Vth sensitivity to tch variation as compared with other orientations. On the contrary, the quantum-confinement effect reduces the Vth sensitivity to L eff, and Si-(111) and Ge-(100) surface show lower Vth sensitivity as compared with other orientations. Our study may provide insights for device design and circuit optimization using advanced FinFET technologies.