A method of manufacturing an organic thin film transistor characterized by low costs and high performances, the method in which the self-assemble monolayer is formed in a short period of time, and the organic thin film transistor are provided. A method of manufacturing an organic thin film a transistor having a gate electrode, a semiconductor layer, a source electrode, and a drain electrode on a substrate, wherein a semiconductor solution as a mixture of the self-assembled monolayer material and organic semiconductor material is coated between the source electrode and drain electrode, whereby a semiconductor layer is formed.