To easily obtain gallium nitride thin film in particular by a sputtering method using a gallium cooled to a specified temp. or below as a target.

Since gallium becomes a solid at ≤29°C, in this state, sputtering is executed by using it as a target. As the sputtering method, a magnetron sputtering method or the like can be used. For keeping this target at ≤29°C in a sputtering device, e.g. a method of cooling a cathode electrode to be mounted with the target by a closed loop cooling system or the like can be used. As the sputtering gas, for obtaining gallium nitride thin film, a gaseous mixture added with nitrogen or nitrogen gas only is used. Moreover, in the case tight adhesion and the improvement of crystallinity are required, the substrate temp. at the time of the film formation is regulated to 250 to 790°C. Furthermore, in the case the removal of residual oxygen in the film is needed, execution of a reducing reaction treatment in a hydrogen or hydrogen plasma atmosphere after the film formation can cause an improvement.