We present a comparative study of InGaAs/InAlAs high electron mobility transistors (HEMTs), intended for cryogenic ultra-low noise amplifiers (LNAs) and fabricated on different substrate and buffer technologies. The first was pseudomorphically grown on InP (InP pHEMT) while the second was grown on a linearly graded metamorphic InAlAs buffer on top of a GaAs substrate (GaAs mHEMT). Both HEMTs had identical active epitaxial regions. When integrated in a 4-8 GHz 3-stage LNA at 300 K, the measured average noise temperature was 45 K for the InP pHEMT and 49 K (9% higher) for the GaAs mHEMT. When cooled down to 10 K, the InP pHEMT LNA was improved to 1.7 K whereas the GaAs mHEMT LNA was only reduced to 4 K (135% higher). The observed superior cryogenic noise performance of the HEMTs grown on InP is believed to be due to a higher carrier confinement within the channel. Microscopy analysis suggested this was related to defects from the metamorphic buffer of the GaAs mHEMT. (C) 2013 Elsevier Ltd. All rights reserved.