A method of forming a copper oxide film including forming a copper oxide film including an ammonia complex by causing a mixed solution of aqueous ammonia and aqueous hydrogen peroxide, which has been adjusted to have pH of 8 to 10 or pH of 9 to 10, to contact a surface of a copper film. A method of fabricating a semiconductor device including burying a copper film to be a wiring or a contact wiring in a wiring groove or a contact hole formed in a surface of an insulating film formed on a semiconductor substrate, or in both the wiring groove and the contact hole, forming a copper oxide film including an ammonia complex on a surface of the copper film by using the copper oxide film forming method, and removing the copper oxide film from the copper film using acid or alkali.