(ZrO 2 ) 0.66 (HfO 2 ) 0.34 dielectric films on p-Si (100) were grown by atomic layer deposition method, for which the conduction band offsets, valence band offsets and band gaps were obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence and conduction band offset values for (ZrO 2 ) 0.66 (HfO 2 ) 0.34 dielectric thin film grown on Si substrate were about 5.34, 2.35 and 1.87 eV, respectively. The band alignment is similar to that of ZrO 2 thin film. In addition, The dielectric function ε(k,ω), index of refraction n and the extinction coefficient k for the (ZrO 2 ) 0.66 (HfO 2 ) 0.34 thin films were obtained from a quantitative analysis of REELS data by comparison to detailed dielectric response model calculations using the QUEELS-ε(k,ω)-REELS software package. These optical properties for (ZrO 2 ) 0.66 (HfO 2 ) 0.34 thin films are similar to that of ZrO 2 dielectric thin films.