An organic thin film transistor includes a drain electrode, a semiconductor layer, a source electrode, a gate insulator, and a gate electrode. A horizontal portion and a vertical portion of the semiconductor layer are respectively located on a top surface and an end surface of the drain electrode, and the drain electrode protrudes from the horizontal portion in a first direction. The source electrode is disposed along a surface of the semiconductor layer. The source electrode has an extending portion that extends in a second direction opposite to the first direction. The gate insulator is disposed along a top surface and two side surfaces of a stacked structure defined by the drain electrode, the semiconductor layer, and the source electrode. The gate electrode is located on the gate insulator, and a portion of the gate insulator is between the stacked structure and the gate electrode.