We present a detailed analysis of the trap states in atomic layer deposition Al2O3/InAIN/GaN high electron mobility transistors grown by pulsed metal organic chemical vapor deposition.Trap densities,trap energies and time constants are determined by frequency-dependent conductance measurements.A high trap density of up to 1.6 × 1014 cm-2eV-1 iS observed,which may be due to the lack of the cap layer causing the vulnerability to the subsequent high temperature annealing process.