A method for forming a capacitor of a semiconductor device having a dielectric film of high dielectric constant having three-dimensional structure for securing capacitance of semiconductor device in order to have excellent deposition characteristics, by forming a storage electrode formed of Ru film on a semiconductor substrate and forming dielectric films formed of high dielectric constant materials having excellent step coverage on the surface of the storage electrode, the dielectric films having a stacked structure of a first dielectric film formed at low deposition speed and a second dielectric film formed at higher deposition speed by reducing the amount of added gas, thereby performing the subsequent process easily and improving yield and productivity of semiconductor device and then embodying high integration of semiconductor device.