Provided are an organic thin film transistor having high bendability and high stability in air and a method of manufacturing the organic thin film transistor. The organic thin film transistor includes: a gas barrier layer consisting of a resin layer and an inorganic layer; a transistor element that is formed on one main surface side of the gas barrier layer and includes a gate electrode, an insulating film, an organic semiconductor layer, a source electrode, and a drain electrode; and a sealing layer that is laminated on a side of the transistor element opposite to the gas barrier layer through an adhesive layer, in which a thickness of the resin layer in the gas barrier layer is less than a thickness ranging from the inorganic layer to the sealing layer in the gas barrier layer.