In a method of forming an oxide superconductor/semiconductor junction between an oxide superconductor and a semiconductor containing bismuth or thallium, an atomic layer of silver of no more than 3 atoms thickness is formed by vapor deposition of silver on the surface of the semiconductor, an atomic layer of bismuth or thallium of no more than 3 atoms thickness is formed by vapor deposition of bismuth or thallium on the silver layer, the double atomic layer consisting of silver and bismuth or of silver and thallium are heated to form a layer wherein the atoms of silver and bismuth or silver and thallium are arranged regularly on the surface of the semiconductor, and the oxide superconductor is formed to a specified thickness on the regularly arranged layer.