A method for manufacturing an organic semiconductor element capable of obtaining an organic semiconductor element in which an organic semiconductor layer is patterned without lowering the mobility of the organic semiconductor layer through a simple and easy process, which includes: an organic semiconductor layer formation step; a first dielectric layer formation step of forming a first dielectric layer on the organic semiconductor layer to be positioned at least on a channel region between the source electrode and the drain electrode; and a second dielectric layer formation step, wherein the second dielectric layer has a contact portion contacting the organic semiconductor layer around the first dielectric layer, and a mixed layer in which the organic semiconductor layer and the second dielectric layer are mixed with each other is formed to constitute an interface between the organic semiconductor layer and the second dielectric layer in the contact portion.