The paper presents the results of characterization of MOS structures with aluminum oxide layer deposited by ALD method on silicon carbide substrates. The effect of the application of thin SiO2 buffer layer on the electrical properties of the MOS structures with Al2O3 layer has been examined. Critical electric field values at the level of 7.5–8 MV/cm were obtained. The use of 5 nm thick SiO2 buffer layer caused a decrease in the leakage current of the gate by more than two decade of magnitude. Evaluated density of trap states near the conduction band of silicon carbide in Al2O3/4H-SiC MOS is about of 1×1013 eV−1cm−2. In contrast, the density of the trap states in the Al2O3/SiO2/4H-SiC structure is lower about of one decade of magnitude i.e. 1×1012 eV−1cm−2. A remarkable change in the MOS structure is also a decrease of density of electron traps located deeply in the 4H-SiC conduction band below detection limit due to using of the SiO2 buffer layer.
 M. Levinshtein, S. Rumyantsev and M. Shur, Handbook Series on Semiconductor Parameters: Volume 2: Ternary And Quaternary III-V Compounds, World Scientific, London, 1996, 1999.
 B.J. Baliga., Silicon Carbide Power Devices, World Scientific, Singapore, 2006.
 D. Okamoto, H. Yano, K. Hirata, T. Hatayama and T. Fuyuki, “Improved inversion channel mobility in 4H-SiC MOSFETs on Si face utilizing phosphorus-doped gate oxide”, IEEE Elec. Dev. Let., 31(7), 710–712 (2010).
 J. Robertson, “High dielectric constant gate oxides for metal oxide Si transistors”, Rep. Prog. Phys. 69, 327–396 (2006).
 K.Y. Cheong, J.H. Moon, H.J. Kim, W. Bahng and N.K. Kim, “Analysis of current conduction mechanisms in atomic-layer-deposited Al2O3 gate on 4H silicon carbide”, App. Phys. Let. 90, 162113 (2007).
 K.Y. Cheong, J.H. Moon, T.J. Park, J.H. Kim, C.S. Hwang, H.J. Kim, W. Bahng and N.K. Kim, “Improved electronic performance of HfO2/SiO2 stacking gate dielectric on 4H SiC”, IEEE Tran. on Elec. Dev. 54(12), 3409–3413 (2007).
 A. Taube, K. Korwin-Mikke, T. Gutt, T. Małachowski, I. Pasternak, M. Wzorek, A. Łaszcz, M. Płuska, W. Rzodkiewicz, A. Piotrowska, S. Gierałtowska, M. Sochacki, R. Mroczyński, E. Dynowska and J. Szmidt, “Fabrication and characterization of hafnium oxide thin layers for application in silicon carbide MOSFET technology”, Elektronika, 52(9), 117–120 (2011).
 Y. Seo, S. Lee, I. An, C. Song, and H. Jeong, “Conduction mechanism of leakage current due to the traps in ZrO2 thin film”, Semicond. Sci. Technol. 24, 115016 (2009).
 C.M. Tanner, Y.Ch. Perng, C. Frewin, S.E. Saddow and J.P. Chang, “Electrical performance of Al2O3 gate dielectric films deposited by atomic layer deposition on 4H-SiC”, App. Phys. Let. 91, 203510 (2007).
 L.M. Terman, “An investigation of surface states at a silicon/silicon oxide interface employing metal-oxide-silicon diodes”, Solid-State Electron. 5, 285 (1962).
 K.Y. Cheong, J.H. Moon, D. Eom, H.J. Kim, W. Bahng, and N-K. Kim, “Electronic properties of atomic-layer-deposited Al2O3/thermal-nitrided SiO2 stacking dielectric on 4H SiC”, Electrochem. Solid-State Lett., 10(2), H69-H71 (2007).