SiCOI (SiC On Insulator) composite substrates obtained by the Smart-Cut(TM) process are alternative possible substrates for epitaxial growth of Wide Band Gap (WBG) materials such as GaN and GaN alloys. Similar to bonded SOI structure, the SiCOI structures basically comprises a thin film of single SiC crystal bonded onto a substrate such as, for instance, silicon. Additionally to the well known insulation properties, SiCOI substrates have proven to be adapted to the growth of high quality GaN layers. This first study has proven compatibility of SiCOI structures for single layer GaN MBE growth. We present here lastest results of AlGaN / GaN HEMT structures grown by MBE with NH3 as nitrogen precursor onto SiCOI (on silicon) structure realised by Smart Cut(TM). First of all, complete SiCOI structure realisation will be described and typical physical characterization results will be presented for this kind of substrate. Then, MBE epitaxy set-up and growth parameters for HEMT structure will be detailed, including specific buffer layer stack description. Finally, physical and electrical characterisation results for epi-layers and HEMT structure will be presented. Those results show strong compatibility of the SiCOI structure for MBE epitaxy of GaN based HEMT structure and demonstrate the interest of the Smart Cut(TM) approach to build composite substrates, like SiCOI, for hetero-epitaxy application.