We have investigated the electron mobility limited by the remote charge scattering, μ RCS, in the thin silicon body (≤8 nm) double-gated metal- oxide-semiconductor field-effect transistors (MOSFETs), focusing on its dependency on the body thickness and the silicon surface orientation. In order to predict the μ RCS in such an unprecedented MOSFET system, the adequacy of physical models used in the computation was verified by comparing the computational results with the experimentally determined μ RCS from the actual bulk MOSFETs with high-k dielectric fabricated on the (100) and (110) silicon substrates. It has been discovered for the first time that the μ RCS is dropped to less than half of the bulk device's μ RCS when the body thickness is 5 nm and that the μ RCS lowering derived from the body thickness reduction is more serious in the (110)-oriented surface than in the (100)-oriented surface. These mobility trends have been quantitatively explained by the effective mass difference between the two surfaces as well as by the carrier confinement in the metallurgically defined narrow silicon body. These observations indicate the great importance of the systematic reduction of charged traps in high-k gate dielectrics in the advanced devices. © 2012 The Japan Society of Applied Physics.