Example embodiments of the present invention for fabricating an organic thin film transistor including a substrate, a gate electrode, a gate insulating layer, metal oxide source/drain electrodes and an organic semiconductor layer wherein the metal oxide source/drain electrodes are surface-treated with a self-assembled monolayer (SAM) forming compound containing a sulfonic acid group. According to example embodiments of the present invention, the surface of the source/drain electrodes may be modified to be more hydrophobic and/or the work function of a metal oxide constituting the source/drain electrodes may be increased to above that of an organic semiconductor material constituting the organic semiconductor layer. Organic thin film transistors fabricated according to one or more example embodiments of the present invention may exhibit higher charge carrier mobility. Also disclosed are various example devices including display devices having organic thin film transistors made by example embodiments of the present invention.