The RF performance of lattice-matched InAlN/GaN heterostructure field-effect transistors (HFETs) and Al2O3/InAlN/GaN metal-oxide-semiconductor HFETs (MOSHFETs) with varied gate length was evaluated. The current gain cutoff frequency fT and the maximum oscillation frequency fmax for the HFETs with 0.3-μm gate length were 54 and 58 GHz, respectively. An increase of fT to 61 GHz and offmax to 70 GHz was obtained for the MOSHFETs. The HFETs and MOSHFETs with different gate length yielded an fT ?? LG product of 18 and 21 GHz ?? μm, respectively. These are higher values than reported yet on InAlN/GaN devices and similar to those known for AlGaN/GaN HFETs.