Abstract In this study, spray-coating has been opted to prepare patterned Poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes for an organic thin film transistor (OTFT). The conducting polymer was grown via the vapor phase polymerization (VPP) method. The film quality of VPP-PEDOT critically relies on the uniformity of oxidant film selectively patterned on a thermally oxidized Si-wafer surface prior to the polymerization. Therefore, to improve the uniformity of the oxidant film, this study tried to discover best conditions of spray-coating. Several different temperatures of Si-wafer substrate, distances from nozzle to wafer, and spray times were tested during the spray coating process. Then, sprayed oxidant films and vapor phase-polymerized PEDOT patterns were characterized by several thin film analyzing tools such as FE-SEM and optical microscope. The characterization found that the best conditions of spray coating are room temperature, 18cm, and 50s of substrate temperature, spray distance, and time, respectively.