We report on the plasma-assisted molecular-beam epitaxy growth and device characteristics of InAlN/GaN heterostructure field-effect transistors (HFETs). The In mole fraction in InAlN was estimated to be 0.15 from the X-ray diffraction profile. The surface root-mean-square roughness of the InAlN layer was less than 3 nm. The room-temperature Hall mobility was 654 cm²/V·s, and the sheet electron density was 1.7 ×10¹³ cm^-2. The InAlN/GaN HFET, which had a source-drain spacing of 3 µm and a gate length of 1.5 µm, showed a good pinch-off characteristic. The maximum source-drain current density and extrinsic transconductance were 500 mA/mm and 52 mS/mm, respectively.