According to example embodiments, a method of manufacturing an organic thin film transistor includes sequentially forming a gate electrode, a gate insulator, a source electrode, and a drain electrode on a substrate, forming a first self-assembled monolayer on the source electrode and the drain electrode from a first self-assembled monolayer precursor, forming a second self-assembled monolayer on the gate insulator from a second self-assembled monolayer precursor that is different from the first self-assembled monolayer precursor, and forming an organic semiconductor on the first self-assembled monolayer and the second self-assembled monolayer. The first self-assembled monolayer and the second self-assembled monolayer may be formed simultaneously or sequentially in a single container. An organic thin film transistor may be manufactured according to the method. A display device may include the organic thin film transistor.