In this paper, together with the accompanying Part I, an easy-to-implement electron mobility model which accurately predicts low-field mobility in bulkMOSFETs and UTB-SOI FETs fabricated on different crystal orientations is developed. In Part I, the general features of the model have been presented. In this Part II, the effects induced by extremely-small silicon thicknesses are addressed, namely, the scattering induced by interface states and silicon thickness fluctuations, intervalley-phonon scattering suppression, and surface optical phonons. Besides, corrections necessary for double-gate FETs are considered. This allows to extend the validity of the model presented in Part I to single and double-gate FETs with silicon thicknesses as small as about 2.5 nm.