For the first time, the high frequency (HF) performance of an ultra-thinned body (UTB) fully depleted silicon-on-insulator (FDSOI) incorporating TiN/HfO 2 gate stack is reported. Full small signal equivalent parameters of UTB-FDSOI are extracted and analysed in detailed. It is revealed that UTB-FDSOI with longer unit width W U (same total width W TOT ) results in slightly higher g m that leads to better HF performance. Despite of the mobility degradation due to the quality of the interface between the high-K dielectric and silicon, the measured transition frequency (f T ) still corresponds well to that predicted from the ITRS roadmap. Optimising the gate stack for low R G is crucial as huge R G in the current technology is the key parameter responsible for the low f MAX obtained. This work can also be considered as the first ever experimental device measured suitable to be used for the Low STand-by Power (LSTP)-based RF/mobile application.