To introduce a new micro-safing sensor for automotive applications with excellent characteristics based on silicon micro-machining techniques to prevent malfunctions in air bag systems using an acceleration switch. This sensor is composed of an upper electrode, cantilever, and pedestal formed by silicon micro-machining. The upper electrode and cantilever contact mechanically when acceleration during collision is applied and the “ON” signal is output. To achieve a satisfactory result, we developed an optimal shape design using FEM simulation. Also, the frequency characteristic of 100Hz and threshold acceleration of 2-4 (G) are obtained by electrostatic force and chattering measure at the contact point. Other characteristics include high-speed response, compactness, and the fact it is inexpensive, making it highly suitable as a safing sensor for side air bag systems.