A semiconductor device and a method for forming the same. A dielectric layer is formed on a semiconductor substrate or on a lower electrode of a capacitor. Vacuum annealing is performed on the dielectric layer. Thus, impurities remaining in the dielectric layer can be effectively removed, and the dielectric layer can be densified. As a result, the electrical characteristics of the semiconductor device are improved. For example, the leakage current characteristics of the dielectric layer are improved and capacitance is increased.