Abstract: The present disclosure provides a method for fabricating a vertical heterojunction of metal chalcogenides. The method includes steps of providing a multi-layer material, performing an ion implantation and performing an annealing. The multi-layer material has a carrier and a metal layer, in which the metal layer covers the carrier to form an interface. The carrier includes an oxide of a first metal element, and the metal layer includes a second metal element. The step of performing the ion implantation is to inject a chalcogen ion source into the multi-layer material to allow a plurality of chalcogen ions to be implanted in a depth area of the multi-layer material, and the depth area includes the interface. The step of performing the annealing is to form a first metal chalcogenide and a second metal chalcogenide at two sides of the interface, respectively.