We present and apply a control methodology using the divergence of the system as a goal function to control semibatch chemical reactors and show how the process operation may be optimized by only measuring the reactor and jacket temperatures. The implementation of the approach is also demonstrated using phase-space reconstruction techniques. This new control methodology offers a complementary approach to more traditional techniques and it can be easily extended to other industrial installations and processes. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.