In situ measurements of static characteristics for an ad-hoc silicon-on-insulator (SOI) device represent an important method for SOI technologies characterisation. The Separation by IMplanted OXygen (SIMOX) technique is based on oxygen ions implantation into Si-film. After annealing, an increased doping concentration was reported, because of the residual oxygen clusters within the film, giving rise to oxygen thermal donors. Therefore this study offers an original algorithm for doping concentration estimation in these SOI films. A specific device used for in situ electrical characterisation of SOI wafers is the pseudo-metal oxide semiconductor (MOS) transistor. In this study, the doping concentrations extraction is based on graphical solution of a non-linear equation and third-order derivative zeroing of the measured static characteristics. In this scope, experimental curves ID-VG, in inversion and accumulation were experimentally measured for a pseudo-MOS transistor made in SIMOX technology. In this situation, the threshold and flat-band voltage are extracted, free of classical conventions. The extracted doping concentration in film is roughly 5.8 × 1015 cm- 3; also the conductivity is changed from p to n in film, as the literature predicted.