A method of manufacturing a semiconductor package includes: forming a strip substrate including a plurality of unit substrates, each being provided with a first connection pad and a second connection pad on a first surface of the unit substrate and each unit substrate being electrically and physically isolated from each other with the intervention of saw lines, first ground connection pads formed on the respective unit substrates, each of the first ground connection pads being electrically coupled with the first connection pad over the respective unit substrates, second ground connection pads formed on the saw line on the first surface side of the unit substrates and electrically isolated from the unit substrates, and test wiring formed on the saw line, the test wiring being electrically isolated from the unit substrates and electrically coupled with the second ground connection pads; and attaching semiconductor chips onto the respective unit substrates.