Ultra-Thin Body and Box (UTBB) Fully-depleted Silicon-on-Insulator (FDSOI) MOSFETs exhibit very high transit frequency granting advantageous RF and low-power circuits design. This requires accurate models describing transistor behavior in all operating regimes including low levels of MOSFET channel inversion. In this paper, Leti-UTSOI based RF model will be compared against electrical measurements from 28nm FDSOI devices operating down to low bias conditions. The outcome demonstrates the accuracy and efficiency of Leti-UTSOI for low-power and RF applications design.