A novel MEMS device architecture: the SOI SG-MOSFET, which combines a solid- state MOS transistor and a suspended metal membrane in a unique metal-over- gate architecture, is proposed. A unified physical analytical model (weak, moderate and strong inversions) is developed and used to investigate main electrostatic characteristics in order to provide first-order design criteria for low-voltage operation and high-performance. It is demonstrated that the use of a thin gate oxide (<20 nm) is essential for a high C_on/C_off (>100) and a low spring constant (<100 N/m) is needed for low voltage (<5 V) actuation. An adapted fabrication process is reported.