Bismuth(III) oxide has been successfully applied as a photocatalyst in the arylation of heteroarenes starting from diazonium salts. With a low catalyst loading (1 to 5 mol%), this cheap and nontoxic semiconductor could efficiently promote the formation of the aryl radical under visible light irradiation. The phenylated products were obtained in moderate to good yields, even in a 10 mmol scale. In two cases, the diazonium salt was generated in situ and directly used in catalysis. Besides heteroarenes, Bi2O3 proved also to catalyze the arylation of differently substituted alkenes and alkynes, thus representing a viable and practical alternative to the more commonly used ruthenium complexes and organic dyes.