In this paper, together with the accompanying Part I, an easy-to-implement electron mobility model that accurately predicts low-field mobility in bulk MOSFETs 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. These effects include 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 the validity of the model presented in Part I to be extended to single- and double-gate FETs with silicon thicknesses as small as about 2.5 nm.