This work provides a detailed study of 28 nm fully-depleted silicon-on-insulator (FD-SOI) planar ultra-thin body and BOX (UTBB) MOSFETs for high frequency applications. All parasitic elements such as the parasitic gate and source/drain series resistances, total capacitances are extracted and their effects on RF performance are analyzed and compared with previous work on similar devices. Two main RF figures of merit (FoM) such as the current gain cut-off frequency (f(T)) and the maximum oscillation frequency (f(max)) are determined. It is shown that f(T) of similar to 280 GHz and f(max) of similar to 250 GHz are achievable in the shortest devices. Based on the extracted parameters, the validation of the small-signal equivalent circuit used for modeling UTBB MOSFETs is investigated by comparing simulated and measured S-parameters. (C) 2015 Elsevier Ltd. All rights reserved.