Two BiCMOS processes were adapted for SOI and the performance of the bipolar devices was studied. Differences in electrical parameters were observed, in particular the current gain, which processing or doping profiles could not explain, but correlated with observed stress in transistors. Simulation of the process flow with stress included revealed that stress was generated to a higher degree in the SOI wafers in the presence of deep trench isolation (DTI). Theoretical estimations and electrical simulations with and without stress yielded results consistent with observed data. Thus, we conclude that the observed differences are caused by process-induced in-plane biaxial stress.