Provided are methods of fabricating capacitors of semiconductor devices, the methods including: forming a lower electrode on a semiconductor substrate, performing a pre-process operation on the lower electrode for suppressing deterioration of the lower electrode during a process, forming a dielectric layer on the lower electrode using a source gas and an ozone gas, and forming an upper electrode on the dielectric layer, wherein the pre-process operation and the forming of the dielectric layer may be performed in one device capable of atomic layer deposition.