Transfer technology is now becoming very attractive not only for new technologies such as flexible technology but also for solid state technologies when performances are limited by technological barriers that have to be overcome. In this last context, the transfer of high electron mobility transistors (HEMTs) on diamond substrates represents an opportunity to improve the thermal dissipation when the device operates at high radio frequency power levels. Up to now, the technological process for the transfer of these transistors is not detailed in the literature. In this article, the first demonstration of AlGaN/GaN HEMTs on diamond substrates by transfer technology obtained through sputtered aluminum nitride (AlN) layers bonding at low temperature is reported. Devices are first fabricated on AlGaN/GaN epilayers grown on silicon (Si) substrates. Afterward, AlGaN/GaN thin films with devices are released from the Si growth substrate and transferred at 160 °C onto a diamond substrate thanks to an AlN bonding layer. A full description of the transfer technology and all the technological limits and risks are presented. The transferred device provides a maximum DC drain current density I_{DS Max} of 690 mA mm^-1 at V_GS = 0 V. Furthermore, a cutoff frequency f_T of 85 GHz and a maximum oscillation frequency f_MAX of 106 GHz are extracted from S-parameter measurements.