Electrostatically operated micro torsion mirrors for a new concept of optical switching matrix is presented. The structure is composed of a mirror (400/spl mu/m x 400/spl mu/m in area and 30/spl mu/m in thickness) and torsion beams (14/spl mu/m wide, 320,/spl mu/m long, and 0.3/spl mu/m thick). The torsion mirror is free-standing over a through hole made by reactive ion etching of the substrate from the backside. Owing to double-step RIE, there is a silicon mesa only on the backside of the mirror to keep it flat and rigid, A diaphragm of silicon oxide is employed as a temporary support to successfully release fragile structures. Characteristics of electrostatic operation were determined.