The data provided here has been used in the preperation of figures for the following manuscript: T. Partida-Manzanera, Z.H. Zaidi, J.W. Roberts, S.B. Dolmanan, K.B. Lee, P.A. Houston, P.R. Chalker, S. Tripathy, and R.J. Potter, Comparison of atomic layer deposited Al2O3 and (Ta2O5)0.12(Al2O3)0.88 gate dielectrics on the characteristics of GaN-capped AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors, J. Appl. Phys. 126, 034102 (2019); DOI: 10.1063/1.5049220 Experimental procedure: Please see paper for details DATA FILE DETAILS: FILE TYPES: Numerical data is provided as .CSV files. FILE NAMING: File names are directly related to the figure numbers used in the manuscript. DATA HEADINGS: The first row of each column in the .CSV files contains a clear description of the data within the column together with units in brackets.