This paper presents the derivation, implementation and validation of a new model for Surface Roughness Scattering (SRS) in multi-gate FETs (MuGFETs) and gate-all-around nanowires (GAA-NW) FETs. The model employs a non linear relation between SRS matrix elements and interface fluctuations, that in planar MOSFETs allowed us to reconcile mobility simulations with experimental values for the r.m.s. interface roughness \Delta_rms. The model is formulated for fairly arbitrary cross-sections and biasing conditions.
