The harmonic and intermodulation distortions of both fully-depleted (FD) and partially-depleted (PD) silicon-on-insulator (SOI) MOSFETs are studied. The analysis is based on the recently developed integral function method and the results are compared to a third-order Volterra model of the MOSFET. This modelling helps us to understand the non-linear mechanisms of the considered devices and to predict their frequency behaviour. The models are validated through large-signal network analyser measurements. The devices performances are discussed.