A method for manufacturing a semiconductor device, includes: a preparation step, a flow step, and a processing step. The preparation step prepares an etching solution by dissolving titanium in an ammonia-hydrogen peroxide solution in advance before use of the ammonia-hydrogen peroxide solution for etching. The flow step flows the etching solution after the preparation step so that a concentration of the etching solution in a processing bath is constant. The processing step etches a metal film on a semiconductor wafer with the etching solution by putting in the processing bath the semiconductor wafer having a resist film and the metal film after the flow step is started. The metal film is preferably formed of titanium, and a temperature of the etching solution is preferably adjusted by flowing the etching solution so that the etching solution flows via a temperature controller.