[en] Highlights: • New features in low frequency capacitance curves of MIS heterostructures based on AlGaN/GaN have been observed. • Ideal low-frequency and high-frequency capacitance curves were simulated. • Simulated low-frequency capacitance curves have the same shape as experimental curves. • The new capacitance features may be the result of interface traps that are able to follow the measuring signal. Influence of interface traps at Al₂O₃/(GaN)/AlGaN interface on low and high frequency capacitance of Al₂O₃/(GaN)/AlGaN/GaN heterostructure capacitor was studied. New features were observed in the capacitance curves. Obtained experimental results were modeled and simulated and accordance with the experiment has been obtained. For lower frequencies a new capacitance peak in the depletion and increase of the capacitance in a plateau region were measured. The capacitance peak in the depletion region was successfully explained by a capacitance response of the interface traps with U-shape density distribution. On the other hand the increase of the capacitance plateau was modeled by the homogeneous interface trap distribution. We assume that the traps located near the band edges having the highest density are able to respond to the low frequency measuring.