A method for forming a metal bump is provided. Firstly, a photo-resist layer is formed on an IC chip by using a lithographic process. The photo-resist layer comprises a metal bump reserved groove and a metal bump slit reserved portion with the extent covering a metal pad. The metal bump slit reserved portion is formed on the metal pad and within the metal bump reserved groove. Then, a deposition process is applied to form the metal bump in the metal bump reserved groove and have the metal bump slit reserved portion penetrating the metal bump. Afterward, the photo-resist layer is removed to leave the metal bump with a metal bump slit therein.