The successful fabrication of InAlSb/InAs and InAlSb/InAsSb HFETs using recessed gate technology is reported. Epitaxial growth, device fabrication and characterisation are discussed in this Letter. A comparison of the two kinds of HFETs shows that the use of Sb in the InAs channel layer can effectively reduce the gate leakage resulting from the band-to-band tunnelling. This improvement is primarily because of increased separation between the conduction band edge of the InAsSb channel layer and the valence band edge of the InAlSb top barrier layer. An InAlSb/InAsSb HFET with 2 μm gate length and 50 μm gate width shows ID = 596 mA/mm and gm = 1 S/mm.