The present invention discloses a method for fabricating a capacitor for a semiconductor device. The method includes the steps of: forming a lower electrode at the upper portion of a semiconductor substrate where a predetermined structure has been formed; forming an amorphous (Ta2O5)1−x—(TiO2)x film on the lower electrode; performing a thermal treatment on the amorphous (Ta2O5)1−x—(TiO2)x film; and forming an upper electrode on the amorphous (Ta2O5)1−x—(TiO2)x film. A capacitance for the operation of a high integration device is sufficiently obtained by using the (Ta2O5)1−x—(TiO2)x film having a high dielectric constant, thereby fabricating the capacitor suitable for the high integration semiconductor device.