In this paper we analyse a kick-out model for impurity diffusion in compound semiconductors. The form for the model described here has not previously appeared in the literature. The substitutional impurities are fixed to be singly negatively charged while the self-interstitials are taken to be neutral. The charge on the interstitial impurity atoms can take any integer value. Both one- and two-dimensional in-diffusion problems are studied. It is found that the impurity diffusion is quite sensitive to the charge on the impurity interstitials.