The sharp peak in the $K^+/\pi^+$ ratio in relativistic heavy-ion collision is discussed. We used the SU(3) PNJL model to show how the splitting of kaon mass can appear in dense matter and how it can affect the kaon to pion ratio. In the model we calculated the $K/\pi$ ratio of both positive and negative charged mesons along the chiral phase transition line to show how the peak position can depend on the phase diagram.