Abstract: The present invention provides a dry etching method, having the steps of introducing a mixed gas consisting of a reactive gas and an inert gas into a plasma chamber for generating a plasma, with the partial pressure of each of these gas components being controlled, exciting the mixed gas within the plasma chamber so as to generate ionized particles and excited particles having high reactivity, withdrawing the particles generated in the plasma chamber into a sample chamber having a compound semiconductor substrate housed therein, and physically and chemically etching the compound semiconductor substrate with the particles.