This paper is devoted to the analysis of the electrical processes in SOI SIMOX structures in a wide temperature range (from 4 to 700 K) by a combination of capacitance-voltage and thermally stimulated current techniques. It has been shown that application of such techniques at cryogenic temperatures allows to study the processes in the transition layer and in the buried insulator/substrate interface. Employing a combination of these methods at high temperatures gives the possibility to investigate emission from and trapping at deep traps and to determine the localization of such traps. It has been shown that high-temperature charge instability processes in the buried oxide adversely affect the SOI MOSFET operation.