A novel way to realize UTB GeOI substrates, where the high quality surface layers of Smart-CutTM GeOI is utilized for UTB structure through a layer transfer technology by direct wafer bonding and a GeOI thinning process by the combination of RIE and thermal oxidation, is proposed and demonstrated. The physical properties of the proposed GeOI are systematically evaluated with the thickness down to around 10 nm. The proposed GeOI fabricated and thinned by the present method exhibits better crystal quality than the original one, with preserving the good GeOI thickness uniformity down to the UTB region. The electrical properties of the GeOI structures are also examined by using GeOI pMOSFETs, which are realized with the GeOI thickness down to 11 nm. It is found that the hole mobility of the flipped GeOI is higher at a given GeOI thickness than that of the original GeOI. (C) 2015 Elsevier Ltd. All rights reserved.