A manufacturing method for semiconductor devices includes the steps of forming an Ni/Au film that includes an Ni film and an Au film formed over the Ni film over a wiring that is coupled to each of a plurality of electrode pads formed over a principal surface of a semiconductor wafer and arranges each of the electrode pads at a different position, grinding a back surface of the semiconductor wafer, performing reduction treatment on a surface of the Ni/Au film, and forming a solder bump over the Ni/Au film. In the reduction treatment, respective processes of flux application, reflow soldering and cleaning are performed and the solder bump is bonded to the Ni/Au film after the reduction treatment has been completed. Thereby, bonding reliability in flip chip bonding of a semiconductor device is improved.