In this work, the generalised parametric sensitivity criterion has been applied to isoperibolic-constant jacket temperature-semibatch reactors (SBRs). The results show that the criterion discerns between non-ignition and thermal runaway regions. However, the optimal parametric regions for operating semi-batch processes, called QFS (quick onset, fair conversion and smooth temperature profile) cannot be distinguished from the runaway regions, since both belong to the ignition behaviour. For this reason, a new intrinsic generalised criterion for characterising QFS regions, based on the earliest ignition time of the process, has been developed. The combination of both criteria allows theoretical results to be compared with those existing in literature. Finally, a catalysed esterification reaction is used to compare the simulated and experimental results carried out in a 2 L bench-scale laboratory reactor and in a 100 L pilot plant reactor. These criteria are believed to be of great utility for the thermal stability analysis of isoperibolic SBRs. Furthermore, they can be easily extended to cope with the control system in case of isothermal SBRs. (C) 1998 Elsevier Science S.A. All rights reserved.