It is an object of the present invention to provide a method for manufacturing a highly reliable semiconductor device with preferable yield. In the invention, two-step etching is performed when selectively removing an interlayer insulating film with at least two layers constituting a semiconductor device, and forming an opening. One feature of the invention is that at least either one of a first gas (a first etching gas) and a second gas (a second etching gas) used at the time of the two-step etching is added with an inert gas.