This paper describes the fabrication process of a shrouded turbine and surface modification using fluorinated silane coupling agents to stabilize the charges of a silicon-dioxide electret. The shrouded turbine was fabricated by cavity-through etching, which is deep reactive ion etching (DRIE) through a wafer having cavities made by DRIE and fusion bonding. By using this process, a shrouded turbine with little eccentricity was obtained without damaging the inner structures such as blades and flow ways. Charge stability of electrets was deteriorated by miniaturizing the size. The charge deterioration was caused by leak current through the surface. To decrease the surface conduction, the surface was terminated by fluorine with silane coupling agents. As a result, the charge stability of a silicon-dioxide electret was improved by 100 times compared with HMDS (hexamethyldisilazane) treatment.