The aim of the paper is to analyse the breakdown voltage performance of lateral power devices in silicon on insulator (SOI) technologies. Both silicon on oxide (termed SOI as per the convention) and silicon on sapphire (SOS) technologies have been considered. Detailed numerical modelling together with analytical evaluation has been carried out on lateral devices employing uniformly doped and variation in lateral doping drift regions. The results indicate that existing theories to predict breakdown voltage are valid only in the case of ultrathin insulator layers and fail when ultrathick layers are considered. Predicted results for devices with ultrathick dielectric layers, as it is the case in SOS technology, are presented. Moreover, the breakdown voltage sensitivity with respect to the SOI layer and dielectric thickness is also analysed. (C) 2002 Published by Elsevier Science Ltd.