Electrochemical formation of a Ca-Si film in a molten CaCl2-KCl at 923 K was investigated. Potentiostatic electrolysis of a Si electrode at -0.10 V for 1 h resulted in the formation of a multiphase Ca-Si film having a thickness of about 30 mu m. The Ca-Si film was converted into other alloy phases by anodic potentiostatic electrolysis after the cathodic electrodeposition of Ca metal at -0.10 V. The various transformation reactions and the corresponding equilibrium potentials were clarified. At 923 K, the equilibrium potential was found to be 0.18 V (CaSi2). Reflectance measurements in the ultraviolet, visible, and near-infrared region clarified that the CaSi2 film has a direct bandgap of 3.1 eV. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.