In this work, a study of a batch and semibatch reactor has been carried out based on a very exothermic reaction between thiosulfate and hydrogen peroxide. The experiments were carried out in a glass-jacketed reactor of 5 1, provided with different sensors and a data acquisition system. Thermal and kinetic studies were carried out previously using an adiabatic batch reactor. Then, these results have been used for experiments in semibatch mode of operation with heat transfer. Several experiments have been carried out at different operating conditions (addition flow, initial temperature, initial concentration of reagents...). In batch and adiabatic mode of operation, experimental measures of the reaction mass temperature provided concentration profiles of reagents and products which have been compared to those determined by simulation. In semibatch mode of operation, temperature profiles have also been simulated and validated with experimental results. An algorithm describing the mathematical model has been developed and implemented in a software module written in FORTRAN 77 language. With this mathematical model it has been possible to obtain concentration and heat profiles for the semibatch mode of operation.