For the fabrication of organic transistors sexithiophene (6T) is one of the most promising materials. Since high purity improves the transistor performance of 6T, the FET described here was built on an ultrapure sexithiophene single crystal, shown in the figure as a gray block. The characteristics of this transistor-better than those of FETs based on evaporated polycrystalline sexithiophene-are presented.