A method of manufacturing a semiconductor device in which a semiconductor element 10 is mounted on a substrate 20 through a flip-chip connection, includes the steps of cladding gallium as a bonding material 30 to a connecting pad 22 formed on a surface of the substrate 20, diffusing copper from the connecting pad 22 formed of the copper into the bonding material 30 through heating under vacuum, thereby bringing a state of a solid solution of the gallium and the copper, and aligning a connecting bump 12 formed on the semiconductor element 10 with the connecting pad 22 and bonding the connecting bump 12 to the connecting pad 22 through the bonding material 30 in a state of a solid solution under heating.