We report on InAlN/GaN heterostructure metal-oxide-semiconductor field-effect transistors (MOSHFETs) with an InAlN barrier layer of different compositions (x(InN) 13, 17, and 21%) and ZrO2 gate-insulator/passivation. Static measurements yielded higher drain currents than those on unpassivated HFET counterparts and the currents increased with decreased x(InN). Post deposition annealing of the ZrO2 insulator had less influence on the static performance but remarkable changes were observed on the capacitance-voltage characteristics. The capacitance hysteresis in both channel depletion and barrier accumulation regions was significantly suppressed after annealing. This indicates a reduction of the interfacial trap states and of fixed charge in the oxide. Pulsed current-voltage measurements confirmed this conclusion-the gate lag of only similar to 80% was evaluated for 200 ns pulse width, independently on the composition of the InAlN barrier layer. These results support an application of high permittivity ZrO2 gate-insulator/passivation for the preparation of high-performance InAlN/GaN MOSHFETs. (C) 2013 The Japan Society of Applied Physics