Mobility in high-k/metal-gate Ultra-Thin Body and Box Fully Depleted SOI devices has been extensively investigated by means of multi-scale simulations and experimental data. Split-CV mobility measurements have been performed for various Interfacial Layer Equivalent Oxide Thickness allowing an investigation of the physical mechanisms responsible for the mobility degradation at high-k/Interfacial layer interface. The impact of the back bias on transport properties is investigated and mobility enhancement in the reverse regime (back gate inversion) is studied. A multi-scale simulation strategy is ranging from quantum Non-equilibrium Green’s Functions to semi-classical Kubo Greenwood approach. These advanced solvers made possible a throughout calibration of empirical TCAD mobility models.