The peak observer method is firstly proposed and used for PID type fuzzy logic controllers. In this study, the peak observer method is adapted and then implemented to the classical PI control structure. The basic principle of the method is to change the controller parameters of the system using the peak values of the system response in order to improve system performance. Firstly, the peak observer method is reconsidered on a simple internal model control based classical PI controller. Later, the peak observer method is further developed and a new structure called model based peak observer is proposed and the parameters of PI controller are further tuned for a much better performance. The performances of the proposed methods are tested and compared on different systems based on simulations.