AlGaN/GaN high electron mobility transistor (HEMT) structures were grown on 4H-SiC (0 0 0 1) vicinal substrates with vicinal angles of 0.4 degrees, 1 degrees and 2 degrees inclined toward [10 (1) over bar 0], as well as 0 degrees Oust substrate) by radio-frequency plasma-assisted molecular beam epitaxy (rf-MBE). It was found that the mobility was enhanced by increasing the vicinal angle, particularly, the mobility in the sample grown on a 2 degrees-off substrate exhibited 8600 cm(2)/V s in contrast to that grown on a just sample (3310 cm(2)/V s) at 30 K. In addition, the anisotropic two-dimensional electron gas (2DEG) mobility of the vicinal samples was clearly found, where the mobility at 30 K along the (I 110) direction (parallel to the macro step) and that along (10 (1) over bar 0) direction (perpendicular to the macro step) were 5490 and 1600 cm(2)/V S, respectively, for the 1 degrees-off sample. The enhancement of the 2DEG mobility is considered to be due to the improvement of film qualities by using vicinal substrates. (c) 2006 Elsevier B.V. All rights reserved.