Organic semiconductors offer great promise through their ease of synthesis in a multitude of derivatives, their low temperature processability and their amenability for fabrication of flexible, stretchable and conformable, even imperceptible devices. Nevertheless, the low charge mobility of organic semiconductors remains one of the limiting factors in delivering high performance for organic electronic devices comparable to their inorganic counterparts. In this study, the effects of purification of eight different organic semiconductors (i.e. n-type, p-type, and ambipolar) were determined by means of analyzing their performance improvement in organic field effect transistors. For this purpose, three purity grades of each organic semiconductor were investigated, and devices were fabricated in an identical fashion. It was found that temperature gradient sublimation improves considerably the quality of the organic semiconductors. The results presented here indicate that the purity of the organic semiconductor is a key parameter to be considered in order to achieve high performance for the field of organic field effect transistors.