A gas sensor based on MEMS (microelectro-machine system) has been developed to provide a sensitive means of detecting nitrogen dioxide. The structure, configuration and fabrication steps were described. The sensor was copper phthalocyanine (CuPc) films which caused a resistance change upon exposure to nitrogen dioxide. The sensor demonstrated a good response and recovery time about 4s and 7s separately. Results also indicate to be accordance with the sensitive mechanism of CuPc in terms of semiconductor theory.