To provide a selective etching treatment method which brings about high selectivity by controlling water concentration inside a reaction chamber.

In a semiconductor substrate treatment method for performing etching treatment only for one kind of thin film, selected from among at least two kinds of thin films formed on a semiconductor substrate, by using a semiconductor manufacturing device consisting of a reaction chamber means, a gas inlet means, an exhaust means and a pressure control means, etching treatment consists of a process for introducing HF or HF+H2O into a reaction chamber means by the gas inlet means and at the same time, evacuating it by an evacuation means, and holding the pressure inside a reaction chamber means constant by a pressure control means for restraining the partial pressure rise of water. The selected one kind of thin film is suitably an SiOF film.