Organic heterojunction thin-film transistors are fabricated based on copper phthalocyanine (CuPc) and hexadecafluorophtholocyaninatocopper (F(16)CuPc) as double active layers, which exhibit typical ambipolar conduction. Several substrate temperatures are utilized to tune film morphology, which results in a remarkable change on the electric characteristics of organic transistors. The highest balanced mobility value of 2.91 x 10(-2) cm(2)/V s for hole and 1.04 x 10(-2) cm(2)/V s for electron are obtained by depositing F(16)CuPc at 150 degrees C and CuPc at 200 degrees C, respectively, which are comparable to those conventional single-layer devices. This result demonstrates that the growth conditions of organic heterojunctions play a crucial role in ambipolar devices. (C) 2010 Elsevier B.V. All rights reserved.