Abstract: Micromechanical switches have demonstrated great potential at microwave frequencies due to their very low consumption, low cross modulation, and low insertion loss characteristics. Studies are concentrated on the design of novel structures and fabrication techniques. There is little work that has been done to describe their electrostatic forces modeling. In this paper, an analytical formulation of a membrane switch based on the mechanics of materials is conducted through reasonable assumption and simplification. Furthermore, the sensitivity of switching threshold voltage to switch geometry and material properties is discussed in detail. It would be valuable to design the MEMS switch.