In this paper, we present the investigation of AlGaN/GaN heterostructures deposited on metallic/silver substrates by a novel "combined" two-step epitaxial procedure based on metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). The channel temperature was determined by high lateral and spectral resolution Raman spectroscopy. The characteristics of the structures were compared to those of conventional AlGaN/GaN layers deposited on sapphire. An improved heat dissipation in the metal substrate based HFETs leads to a significant decrease in channel temperature (-60% at 7 W/mm) and affects the long-term stability of the drain current (+2%) favorably in the whole range under investigation (up to 1000h). Metallic substrates are a viable solution toward highly reliable high -power devices and are beneficial to low power electronics as well, where the high integration density also calls for efficient heat dissipation. (C) 2017 Elsevier Ltd. All rights reserved.