The simulation methodology coupling radial ionization profiles issued from Geant4 and the SEE prediction tool MUSCA SEP3 is used to investigate the MBU sensitivity of SOI SRAM cells of different technologies. The simulation approach is first validated against experimental results for a 45 nm SOI SRAM cell, showing very good agreement. The variability of the MBU probability is then studied depending on various parameters. A worst case is identified, for a particular data pattern irradiated with a high LET ion at grazing angle, showing the possibility for three- and four-bit events to occur. The cause for these high multiplicities is identified by examining the cells topology and new design by hardening strategies are proposed to improve the device hardness to MBU, for a 32 nm SOI SRAM cell. The possibilities of the SEE prediction tool for bulk devices are finally discussed.