In QFN packages for vehicles which are required to have high reliability, the side surface of leads is mostly covered with lead-to-lead resin protrusions, which prevent smooth formation of solder fillets during reflow mounting. When the lead-to-lead protrusions are mechanically removed using a punching die, there is a high possibility of causing cracks of the main body of the package or terminal deformation. When a spacing is provided between the punching die and the main body of the package in order to avoid such damages, a resin residue is produced to hinder complete removal of this lead-to-lead resin protrusion. The present invention provides a method for manufacturing semiconductor device of a QFN type package using multiple leadframes having a dam bar for tying external end portions of a plurality of leads. This method includes a step of removing a sealing resin filled between the circumference of a mold cavity and the dam bar by using laser and then carrying out surface treatment, for example, solder plating.