In our opinion, the thermally safe operating conditions for isoperibolic semibatch reactors (SBRs) should be characteristic of two terms: 1. conforming to QFS operating situation; 2. MTSR < MAT. Regretfully, the traditional boundary diagrams are only helpful for designing QFS operating conditions and can't predict the value of MTSR. Hence, the extended boundary diagrams have been developed in this work. Using these extended boundary diagrams, not only QFS operating conditions can be identified, but also MTSR can be predicted. In addition, the predicted MTSR is suggested to add up Delta tau(ta) before checking whether MTSR < MAT, because the value of UA at the end point of dosing period in a realistic case is lower than the ideal value of (UA)(0)(1 + epsilon). By this way conservative results will be obtained. Also, a procedure to identify thermally safe operating conditions for SBRs with the extended boundary diagrams is introduced in the last part. (C) 2018 Elsevier Ltd. All rights reserved.