The present invention provides a method for forming substrates for MOS (metal oxide semiconductor) transistor, comprising the following steps: (A) In a reduced-pressure environment having a pressure lower than 1×10−6 Torr, a base for accomplishing the surface reconstruction and a solid-state metal oxide source is provided, wherein the solid-state metal oxide source is chosen from the group consisting of the following: hafnium oxide, aluminum oxide, scandium oxide, yttrium oxide, titanium oxide, gallium gadolinium oxide and metal oxides of rare earth elements; and (B) vaporize the solid-state metal oxide source in order to make the solid-state metal oxide source become a metal oxide molecular beam and, in a working substrate temperature that is required to achieve an amorphous state of a first metal oxide film, deposit on the base having an amorphous state so as to further fabricate a substrate for MOS transistors.