In this paper, we report the room-temperature and cryogenic properties of true planar 110 nm InAs/AlSb HEMTs fabricated with Ar-ion isolation technology. Device isolation is generally improved and is in particular increased by four orders of magnitude at 6 K compared to 300 K. This results in improved drain current saturation, lower gate leakage current and 23% higher peak transconductance. The RF performance is significantly improved as well, with 47% higher f(T) (162 GHz) and 72% higher f(max) (155 GHz) at the low drain voltage of 0.1 V, compared to room temperature. The overall performance of the fabricated devices shows the suitability of ion implantation for the device isolation at cryogenic temperature. Furthermore, the excellent stability against oxidation and truly planar structure of these devices demonstrate great potential for highly integrated cryogenic millimeter-wave circuits in InAs/AlSb technology with ultra-low power consumption. (C) 2012 Elsevier Ltd. All rights reserved.