The influence of concurrent diffusion of Zn and Si on the interdiffusion on the cation and anion sublattices was studied in InxGa1-xPyAs1-y‐GaAs heterostructures (with x and y≊0.05). The heterostructures are grown by liquid phase epitaxy and the diffusion sources are equilibrium ternary tie triangle sources. The extent of interdiffusion on both group III and V atoms is observed by depth profiling In and P, respectively, with secondary ion‐mass spectrometry. The Zn diffusion selectively enhances the cation (In‐Ga) interdiffusion, whereas Si diffusion enhances both cation and anion interdiffusion to the same extent. A kick‐out mechanism is proposed to explain the selective enhancement of the cation interdiffusion induced by Zn, and a single vacancy mechanism is proposed for the interdiffusion due to Si. Based on those observations, we propose that the impurity diffusion mechanism is a major factor in determining the degree of enhancement.