This paper reports on the influence of material defects on the electrical behaviour of AlGaN/GaN heterostructures grown onto off-axis 4H-SiC. A structural characterization revealed the presence of near-surface V-shaped defects, mostly oriented along the miscut direction [11-20]. High electron mobility transistors with the channel oriented along this direction showed a preferential conduction, while a significant reduction of the drain current occurred only along the orthogonal direction. An electrical analysis allowed us to demonstrate the anisotropy of the mobility of the two-dimensional electron gas.These results are important to predict the optimal device design in AlGaN/GaN heterostructures grown onto misoriented 4H-SiC substrates.