A method for forming a film of an oxide of In, Ga, and Zn, having a spinel crystalline phase comprises providing a substrate in a chamber; providing a sputtering target in said chamber, the target comprising an oxide of In, Ga, and Zn, wherein: In, Ga, and Zn represent together at least 95 at % of the elements other than oxygen, In represents from 0.6 to 44 at % of In, Ga, and Zn, Ga represents from 22 to 66 at % of In, Ga, and Zn, and Zn represents from 20 to 46 at % of In, Ga, and Zn; and forming a film on the substrate, the substrate being at a temperature of from 125° C. to 250° C., by sputtering the target with a sputtering gas comprising O2, the sputtering being performed at a sputtering power of at least 200 W.