A method of manufacture of semiconductor devices is disclosed, which includes an etching process carried out by using an undiluted etching solution containing H2SO4 and NH4F or H2SO4 and HF as main components, and having an H2O content set to 5 wt % or lower. Moreover, a method of manufacture of semiconductor devices is disclosed, which includes selective etching an SiN film by using a mixed solution of H2SO4 and H2O, or an etching solution obtained by adding a small amount of hydrofluoric acid to the mixed solution.