In this paper, we report a novel patterning method for a poly(3,4-ethylenedioxythiophene) (PEDOT) nanofilm deposited on an OTS monolayer-coated silicon wafer substrate by the vapor phase polymerization method. To scrutinize the adhesion improvement, electrical conductivity and feature controllability, patterned PEDOT nanofilms were investigated with a Scotch tape peel test, I-V curve measurement, and optical and atomic force microscopes. The scrutinization strongly indicates that the adhesion improvement is most likely due to direct chemical bonds formed between ethylenedioxythiophene (EDOT) molecules and photo-oxidized OTS monolayer during a vapor phase polymerization reaction. The investigation also discovered that the feature size of the film can be chemically controlled by the reaction between OTS and reactive atomic oxygen gases, and the patterned films generally show a noticeably good electrical conductivity (approximately 500 S/cm at merely approximately 100 nm thick film). These results successfully demonstrate that the patterned PEDOT nanofilms are qualified enough to be employed as an electrode component of an OTFT device since the electrode materials must show an electrical conductivity of at least 50 S/cm or higher.