TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Semiconductor: The zinc-containing metal oxide semiconductor is zinc-tin oxide (Zn2SnO4) of spinel structure, or zinc-titanium-oxide (Zn2TiO4) of spinel structure, in which one or two co-coordinated oxygen atom of zinc oxide tetrahedron is removed to form a zinc-oxide tri-coordinated or two-coordinated structure, to form semiconductor with small band gap and extended functional wavelength in long wavelength region. The metal oxide semiconductor, which does not contain a zinc element, has portion or whole of divalent metallic element in the crystal structure substituted by zinc element. The semiconductor has a support or an electrode for a co-catalyst. The co-catalyst or electrode is noble metal, transition metal and an oxide, preferably platinum, nickel, iridium oxide (IrO2), nickel oxide (NiOx), ruthenium oxide (RuO2). Preferred Compound Semiconductor: The zinc-containing metal oxide semiconductor is zinc oxide of spharelite structure.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Semiconductor: The zinc-containing metal oxide semiconductor is zinc-tin oxide (Zn2SnO4) of spinel structure, or zinc-titanium-oxide (Zn2TiO4) of spinel structure, in which one or two co-coordinated oxygen atom of zinc oxide tetrahedron is removed to form a zinc-oxide tri-coordinated or two-coordinated structure, to form semiconductor with small band gap and extended functional wavelength in long wavelength region. The metal oxide semiconductor, which does not contain a zinc element, has portion or whole of divalent metallic element in the crystal structure substituted by zinc element. The semiconductor has a support or an electrode for a co-catalyst. The co-catalyst or electrode is noble metal, transition metal and an oxide, preferably platinum, nickel, iridium oxide (IrO2), nickel oxide (NiOx), ruthenium oxide (RuO2). Preferred Compound Semiconductor: The zinc-containing metal oxide semiconductor is zinc oxide of spharelite structure.