This paper reports on the modeling and key design aspects of an innovative MEMS device: the suspended-gate MOSFET (SG-MOSFET). Based on the coupled-electromechanical equations describing the suspended gate actuation, we present the investigation of the pull-in voltages and of the capacitance switching and tuning ranges for RF applications. A quasi-analytical model and is developed for the gate-to-substrate capacitance of the SG-MOSFET and then, validated by numerical simulation. A SPICE macro-model using polynomial voltage-controlled source is validates for the DC simulation of the SG-MOSFET. Guidance lines for the low-voltage design of a SGMOSFET RF switch are detailed.