An organic thin film transistor includes a substrate, a source/drain layer that is located on the substrate and has a source region and a drain region, a first buffer layer that is located between the source region and the drain region, a semiconductor layer that is located on the source/drain layer and the first buffer layer, a gate insulating layer, and a gate electrode. The first buffer layer covers at least one portion of the source region and at least one portion of the drain region. The first buffer layer is located among the semiconductor layer, the source region, the drain region, and the substrate. The gate insulating layer covers the source/drain layer and the semiconductor layer. The gate electrode is located on the gate insulating layer, and a portion of the gate insulating layer is located between the gate electrode and the semiconductor layer.