A method for forming metal bumps is disclosed. Steps of the method include supplying a substrate containing a plurality of pads; forming a first photoresist layer on the substrate, herein the first photoresist layer covers the pads; performing a planarization step to remove a portion of the first photoresist layer so as to expose the pads; forming a conductive layer on the first photoresist layer and the pads; electroplating a metal layer on the conductive layer; forming a patterned second photoresist layer on the metal layer; a portion of the metal layer and the conductive layer which are not covered by the patterned second photoresist layer is removed by using the patterned second photoresist layer as a mask; removing the patterned second photoresist layer; and forming a solder mask on the substrate, wherein the solder mask has a plurality of openings to expose the metal layer located on the pads.