A method of manufacturing an organic thin film transistor, the method comprising: a transistor forming step of forming a transistor element on a first gas barrier layer of a transfer type gas barrier film including a substrate and the first gas barrier layer, the transistor element including a gate electrode, an insulating film, an organic semiconductor layer, a source electrode, and a drain electrode, the first gas barrier layer including a resin layer and an inorganic layer, the resin layer being peelable from the substrate, and the inorganic layer being formed on the resin layer; a bonding step of bonding a transfer type gas barrier film including a substrate and a second gas barrier layer to the transistor element through an adhesive layer, the second gas barrier layer including a resin layer and an inorganic layer, the resin layer being peelable from the substrate, the inorganic layer being formed on the resin layer, and the transfer type gas barrier film being bonded such that the inorganic layer side faces the transistor element; and a peeling step of peeling the substrate from each of the two transfer type gas barrier films (40a, 40b), wherein in the bonding step, the transfer type gas barrier film is bonded such that at least one of a thickness (T1, T2) of the resin layer in the first gas barrier layer or a thickness of the resin layer in the second gas barrier layer is less than a thickness ranging from a surface of the inorganic layer of the first gas barrier layer on a side opposite to the resin layer _to a surface of the inorganic layer of the second gas barrier layer on a side opposite to the resin layer. a transistor forming step of forming a transistor element on a first gas barrier layer of a transfer type gas barrier film including a substrate and the first gas barrier layer, the transistor element including a gate electrode, an insulating film, an organic semiconductor layer, a source electrode, and a drain electrode, the first gas barrier layer including a resin layer and an inorganic layer, the resin layer being peelable from the substrate, and the inorganic layer being formed on the resin layer; a bonding step of bonding a transfer type gas barrier film including a substrate and a second gas barrier layer to the transistor element through an adhesive layer, the second gas barrier layer including a resin layer and an inorganic layer, the resin layer being peelable from the substrate, the inorganic layer being formed on the resin layer, and the transfer type gas barrier film being bonded such that the inorganic layer side faces the transistor element; and a peeling step of peeling the substrate from each of the two transfer type gas barrier films (40a, 40b), wherein in the bonding step, the transfer type gas barrier film is bonded such that at least one of a thickness (T1, T2) of the resin layer in the first gas barrier layer or a thickness of the resin layer in the second gas barrier layer is less than a thickness ranging from a surface of the inorganic layer of the first gas barrier layer on a side opposite to the resin layer _to a surface of the inorganic layer of the second gas barrier layer on a side opposite to the resin layer.