Ultra-Ihin body (UTB) SOI MOSFET is promising for sub-50 nm CMOS technologies  However, recent experimental finding  suggests the need for serious reconsiderations of its long-term scaling capability into the sub-10 nm body thickness (TBDDY) regime. Two new phenomena attributed to surface roughness (SR) are identified ; they are enhanced threshold voltage (VTH) shifts and drastic. degradation of mobility with aTBODYdependence [2,3]. In this work, we detail a study of these two phenomena in UTB MOSFETs with sub 10 nm TaODY Si and Ge channels. Firstly, the phenomena of enhanced VTHshifts is modeled by accounting for the fluctuation of quantized energy levels due to SR up to second order approximation. Good corroboration with experimental results  is obtained. Our model is then applied to examine the impact of enhanced VTHshifts on metal gate work function requirements. Secondly, we modeled the SR-limited electron and hole mobility and discuss their impact on the choice of suiface orientations. Mobility anisotropy are also examined for the various surface orientations.