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Noise measurement in the linear regime of the device characteristics shows the evolution of an important Lorentzian-like component in the thin-film SIMOX silicon-on-insulator (SOI) n-MOSFET, during the transition from fully depleted to near fully (or partially) depleted operation. The same noise component co-exists with another Lorentzian-like component commonly observed in the kink region, thus distinguishing it from the latter, which is associated with a shot-noise mechanism. Evidence unambiguously shows that local potential fluctuations, caused by random generation-recombination (G-R) processes at bulk defects in the depleted SOI film, are primarily responsible. Extracted trap energy of ∼0.4-0.45 eV below the silicon conduction band edge confirms the involvement of deep-level electron traps, which are probably linked to the residual oxygen and SiO2 precipitates in the SOI film. A new analytical G-R noise model yields bulk traps with an average density of ∼1016 cm-3, situated at ∼22-32 nm from the front interface. With an area density comparable to that of the front interface states, the proximity of these bulk traps to the conducting channel in thin-film SIMOX SOI devices accounts for the dominance of bulk-trap induced G-R noise over conventional 1/f noise due to near-interface oxide traps.