A copper phthalocyanine (CuPc) thin film based gas sensor with FET structure and channel length 100? m has been prepared by VE method and lithography technique to detect NH3, motor cycle exhaust gases and CO. CuPc material layer was deposited on SiO2 by the vacuum evaporator (VE) method at room temperature and pressure of 8 x10-4 Pa. The stages of manufacturing gas sensor were Si/SiO2 substrate blenching with ethanol in an ultrasonic cleaner, source, and drain electrodes deposition on the substrate by using a vacuum evaporator, thin film deposition between the source/drain and gate deposition. The sensor response times to NH3, motorcycle exhaust gases and CO were 75 s, 135 s, and 150, respectively. The recovery times were 90 s, 150 s and 225, respectively. It is concluded that the CuPc thin film-based gas sensor with FET structure is the best sensor to detect the NH3 gas.