The two-dimensional electron gas (2DEG) mobility limited by dielectric and barrier thickness fluctuations (TF) scattering in Al2O3/AlGaN/GaN double heterojunction high-electron mobility transistors (HEMTs) is calculated. Calculation shows that thickness fluctuation scattering is the main limitation in Al2O3/AlGaN/GaN double heterojunction HEMTs with thin Al2O3 layer thicknesses. In addition, a study of 2DEG mobility as a function of 2DEG density, n(s), shows that TF scattering acts as the main limitation when ns exceeds 2 x 10(12) cm(-2). The results may be used to design HEMTs to obtain higher 2DEG mobilities by modulating the dielectric layer and barrier thicknesses or 2DEG density. (C) 2013 Elsevier B. V. All rights reserved.