Disclosed is a method for synthesizing a transition metal chalcogenide, in which a transition metal chalcogenide is synthesized on a substrate by atomic layer deposition to sequentially supply a precursor of the transition metal chalcogenide and a reactant so as to have a predetermined synthesis thickness, the transition metal chalcogenide is synthesized at a process temperature of 450° C. or higher and 1000° C. or lower, and the transition metal chalcogenide is synthesized at a process temperature corresponding to the predetermined synthesis thickness.