The initial quality of the Silicon-On-Insulator (SOI) wafers is critical for the Low Frequency Noise (LFN) specifications. The LFN is one of the most important parameters for both the analog and the digital circuits. High silicon-buried oxide interface trap concentrations may cause excessive LFN in the circuits. The LFN spectrum can be measured only after the microchips have been manufactured. This book establishes a comprehensive method of evaluating the LFN parameters of the unprocessed SOI wafers utilizing the novel permanent pseudo MOSFET structures. The manuscript provides detailed description of the equipment setup, calibration and procedures of the LFN spectroscopy, paying special attention to the challenges of LFN measurements and the ways of interference elimination. The characterization techniques using the permanent pseudo MOSFET are introduced with the focus on the LFN reduction for SOI circuits. The results for the variety of SOI wafers are presented. This book can be used by students, practicing engineers and scientist as a reference or a studying guide of the LFN issues in SOI circuits.