A semiconductor device comprises a plurality of solder bumps (14) each formed on a pad 13c of a semiconductor device (11). The top of each of the solder bumps (14) is covered with a masking film (16), and the bases of the solder bumps (14) are buried with a reinforcement film (15). The oxidation of the solder bumps (14) is prevented by the masking film (16) and the reinforcement film (16), the latter also undertaking the thermal stress generated between the semiconductor chip (12) and the circuit board (21). The mounting is conducted with the masking film (16) remaining on the top of the solder ball (14), which breaks the masking film (16) and connected to the pad (22) on the circuit board (21).