In this study, we achieved the conversions of Cu–In and Cu–Zn–Sn oxide precursor films to CuInSe 2 and Cu 2 ZnSnSe 4 films, respectively, using SeO 2 as a selenium source in supercritical ethanol (EtOH). EtOH enables sufficient supply of SeO 2 to reaction field due to its high solubility. Moreover, EtOH in high temperature condition reacts with SeO 2 to form diethylselenide, Et 2 Se, and elemental selenium, and shows self-oxidation to release hydrogen. These features of EtOH will contribute to the selenization for the fabrication of the metal-selenide film facilitates the fabrication of metal-selenide film with ideal band gap, even when both precursor film and selenium source are oxides. Supercritical-alcohol-assisted selenization will contribute to the development of the cost-effective non-vacuum fabrication process for metal-selenide in optical devices, such as solar cells.