In this paper, we present the first complete compact model dedicated to Ultra-Thin Body and Box and Independent Double Gate MOSFETs based on an explicit formulation of front and back surface potentials that is valid and extremely accurate in all operation regimes. The model provides physics-based consistent description of DC and AC device characteristics; it has been extensively validated against TCAD and hardware data, and fulfills standard requirements from quality assurance and convergence tests for circuit design.