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 f(T) and the maximum oscillation frequency f(max) for the HFETs with 0.3-mu m gate length were 54 and 58 GHz, respectively. An increase of f(T) to 61 GHz and of f(max) to 70 GHz was obtained for the MOSHFETs. The HFETs and MOSHFETs with different gate length yielded an f(T) x L-G product of 18 and 21 GHz . mu m, respectively. These are higher values than reported yet on InAlN/GaN devices and similar to those known for AlGaN/GaN HFETs.