PURPOSE: A method for fabricating a capacitor of a semiconductor device is provided to save money by eliminating the necessity of a CMP(chemical mechanical polishing) process when a lower electrode is formed and a planarization process is performed, and to more reliably fabricate a capacitor by preventing the surface of the lower electrode from being damaged by a CMP process. CONSTITUTION: A metal layer for a lower electrode is formed on a substrate(20). A buffer layer for an etch-back process is formed on the metal layer for the lower electrode, made of a material having different etch selectivity from that of the metal layer. The metal layer for the lower electrode and the buffer layer are selectively removed to form the lower electrode and a buffer layer pattern. An interlayer dielectric is formed to cover the lower electrode and the buffer layer pattern. An etch-back process is performed to remove the interlayer dielectric to the lower part of the buffer layer. The buffer layer is eliminated. A dielectric thin film is formed on the lower electrode. An upper electrode is formed on the dielectric thin film.