This paper discusses new Random Telegraph Signal (RTS) mechanisms which are typical for Silicon-on-Insulator MOST's. Apart from the standard RTS's which are re ted to the trapping of a single channel carrier by an interface-near oxide trap, there are other causes of RTS-like fluctuations in the drain current of a SOI transistor. It is shown that these phenomena find their origin in trapping by a defect residing either in the thin Si film or in the back oxide. Finally, RTS's can also be rendered visible in thin-film, fully-depleted devices by applying a back-gate bias, i.e. by front-back coupling.