The analysis of the low-frequency noise of fully-depleted Silicon-On-Insulator (SOI) ultra-thin body and Ultra-Thin Buried Oxide (UTBOX) MOSFETs with different gate stacks, Si film thicknesses and extension architecture is performed. It was revealed that the extension architecture is the main factor affecting the drain current and low frequency noise behavior of the devices studied. It is revealed that the 1/f noise of extensionless MOSFETs appears to be higher than for standard ones, especially when the back interface is biased towards accumulation. The latter is accompanied by the lower drain current of extensionless devices in comparison to standard ones. Moreover, the Lorentzians accompanying the Linear Kink Effect that were revealed for standard MOSFETs, were not observed for extensionless devices. The latter is ascribed to the different architecture of the source/drain regions, which affect source/drain-body junctions characteristics and free charge carrier concentration. (C) 2014 Elsevier Ltd. All rights reserved.