Interface traps between dielectric and barrier layers influence the electrical properties of MISHEMT (metal–insulator–semiconductor heterojunction field effect transistor) structures. We demonstrate an approximate method for extraction of the density of interface traps from experimental MISH structures. First, the capacitance curve of an ideal structure without interface traps was generated by fitting the experimental curve in the capacitance plateau and depletion region. Then, the fit in the forward part of the curve was found by a trial and error method using several interface trap distributions. Special U‐shape interface trap distributions were used with different ratio between the magnitudes of the trap densities at the conduction‐band and valence‐band extremes and the middle of the energy gap. A very good fit between the experimental and the theoretical curve has been obtained for the interface trap density 1.3 × 1013 eV−1 cm−2 at the band edges and 1.3 × 1011 eV−1 cm−2 in the middle of the gap.