A method of fabricating by co-sputtering deposition a lanthanoid aluminate film with enhanced electrical insulativity owing to suppression of deviation in composition of the film is disclosed. Firstly within a vacuum chamber, hold two separate targets, one of which is made of lanthanoid aluminate (LnAlO3) and the other of which is made of aluminum oxide (Al2O3). Then, transport and load a substrate into the vacuum chamber. Next, introduce a chosen sputtering gas into this chamber. Thereafter, perform sputtering of both the targets at a time to thereby form a lanthanoid aluminate film on the substrate surface. This film is well adaptable for use as ultra-thin high dielectric constant (high-k) gate dielectrics in highly miniaturized metal oxide semiconductor (MOS) transistors.