An object of the present invention is to provide an organic thin film transistor exhibiting high carrier mobility and a low threshold voltage and having excellent heat resistance, a method of manufacturing an organic thin film transistor, an organic semiconductor composition, an organic semiconductor film, and a method of manufacturing an organic semiconductor film. The organic thin film transistor according to the present invention includes, on a substrate, a gate electrode; an organic semiconductor layer containing an organic semiconductor compound; a gate insulating layer provided between the gate electrode and the organic semiconductor layer; and a source electrode and a drain electrode which are provided to be in contact with the organic semiconductor layer and are connected to each other via the organic semiconductor layer, in which the organic semiconductor layer is in contact with a block copolymer layer containing a block copolymer or further contains the block copolymer, and in which the organic semiconductor compound has a molecular weight of 2,000 or greater and has a repeating unit represented by Formula (1).