A manufacturing method of a semiconductor package includes locating, on a substrate, a semiconductor device having an external terminal provided on a top surface thereof, forming a resin insulating layer covering the semiconductor device, forming an opening, exposing the external terminal, in the resin insulating layer, performing plasma treatment on a bottom surface of the opening, performing chemical treatment on the bottom surface of the opening after the plasma treatment, and forming a conductive body to be connected with the external terminal exposed in the opening.