The present invention relates to a thin film transistor substrate comprising: an insulating substrate; a source electrode and a drain electrode which are formed on the insulating substrate and separated from each other and have a channel area therebetween; a wall exposing at least portions of the source electrode and the drain electrode, respectively, encompassing the channel area, and formed of fluoropolymer; and an organic semiconductor layer formed inside the wall. Thus, the present invention provides a TFT substrate where an organic semiconductor layer is planarized. Further, the present invention also provides a method of making a TFT substrate of which an organic semiconductor layer is planarized.