A method of forming dielectric films including a metal silicate on a silicon substrate comprises a first step of oxidizing a surface layer portion of the silicon substrate and forming a silicon dioxide film; a second step of irradiating ion on the surface of the silicon dioxide film and making the surface layer portion of the silicon dioxide film into a reaction-accelerating layer with Si—O cohesion cut; a third step of laminating a metal film on the reaction-accelerating layer in a non-oxidizing atmosphere; and a fourth step of oxidizing the metal film and forming a metal silicate film that diffuses a metal from the metal film to the silicon dioxide film.