Organic field‐effect transistors that employ copper phthalocyanine (Cu–Pc) as the semiconducting layer can function asp‐channel accumulation‐mode devices. The charge carrier mobility of such devices is strongly dependent on the morphology of the semiconducting thin film. When the substrate temperature for deposition of Cu–Pc is 125 °C, a mobility of 0.02 cm2/V s and on/off ratio of 4×105can be obtained. These features along with the highly stable chemical nature of Cu–Pc make it an attractive candidate for device applications. ©1996 American Institute of Physics.