We report the experimental results of tuning the emission wavelength of InAsInP quantum dots (QDs) by varying either the GaAs interlayer thickness or the indium composition of the Inx Ga1-x As interlayer. The InAs QDs are grown on lattice-matched GaInAsP or InP buffers and are capped with an InP layer. AsP exchange is prominent when the QDs are grown on an InP buffer. A model is developed which considers the AsP exchange, gallium interdiffusion, strain, and barrier height. Our theoretical and experimental results show that gallium interdiffusion and the AsP exchange reaction are mainly responsible for the observed shifts in the QD emission wavelength. The model shows that gallium interdiffusion from the interlayer to the InAs QDs grown on a GaInAsP buffer can be utilized to selectively tune the InAs QD emission wavelength over a wide range.