This paper investigates the intrinsic reliability of ultra-thin buried oxides (UTBOX) integrated in the last generation of FDSOI wafers obtained by the Smart Cut (TM) technology. In term of breakdown reliability, these state-of-the-art UTBOX oxides exhibit comparable performances with thermally-grown SiO2 references. In "the worst case condition", the voltage for a 10 years lifetime of 25 nm thick BOX, is estimated to 14 V, which largely exceeds the maximum operating conditions for back-bias [+3 V, -3 V] in advanced FDSOI integrated circuits. This makes UTBOX family of engineered substrates fully compatible and suitable for multi-V-T applications. (C) 2014 Elsevier Ltd. All rights reserved.