Solvent or solvent composition for organic transistor production, which is excellent in solubility of an organic semiconductor material, and which can form an organic transistor high in crystallinity. The solvent or solvent composition for organic transistor is a solvent or solvent composition for organic semiconductor material dissolution, and includes a solvent ‘A’ represented by the formula (R1)N(R2)—C(═O)—(R3)N(R4) wherein R1 to R4 are the same or different, and each represents a C1-2 alkyl group, or R1 and R4 may be bound to one another to form a ring together with the —N(R2)—C(═O)—N(R3)— moiety as well as an organic semiconductor material.