in a method of forming solder bumps , each solder bump is formed over a corresponding one of a plurality of chip pads of an active upper surface of a semiconductor device . an under bump metallurgy is formed on the upper surface of the semiconductor device and the chip pads . a photoresist layer is deposited thereto and patterned to expose the under bump metallurgy on the chip pads . the solder bumps are formed on the under bump metallurgy exposed from the photoresist patterns , and the photoresist patterns are removed . an intermetallic compound layer is formed on an interface between the solder bump and the under bump metallurgy by heating the solder bump at a temperature lower than a melting point of the solder bump . then , the under bump metallurgy is etched by using the imc as a mask , and the solder bumps are reflowed . the present invention obtains sufficient joint area between the under bump metallurgy and the solder bump as well as joint area between the under bump metallurgy and the buffer layer , and reduces the undercutting of the under bump metallurgy and thereby improves the mechanical and the electrical reliability of the solder bumps .