Field-effect transistor and method for manufacturing same

The present invention achieves, through a simple process, formation of a metal oxide film in a thin-film transistor. A method for manufacturing a field-effect transistor having a gate electrode, a source electrode, a drain electrode, a channel layer, and a gate insulating layer, wherein the channel layer is formed using a metallic-salt-containing composition containing a metallic salt, a polyvalent carboxylic acid having a -C(COOH)=C(COOH)-cis structure, an organic solvent, and water, and in which the molar ratio of the polyvalent carboxylic acid relative to the metallic salt is 0.5 to 4.0.