It is an important way to improve carrier mobility by reducing the contact resistance in organic transistors. In this paper, two kinds of transistors were fabricated with copper phthalocyanine semiconductor. Then by experimental methods, we tested the devices with different structure and different channel length, and analyzed the effect of structure on contact resistance as well as output characteristic. The results demonstrate that gate voltage can effectively reduce the contact resistance in the top contact device.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.