We have theoretically studied the possibility to control the equilibrium solubility of dopants in semiconductor alloys, by strategic tuning of the alloy concentration. From the modeled cases of C-0 in SixGe1-x, Zn- and Cd- in GaxIn1-xP it is seen that under certain conditions the dopant solubility can be orders of magnitude higher in an alloy or multilayer than in either of the elements of the alloy. This is found to be due to the solubility's strong dependence on the lattice constant for size mismatched dopants. The equilibrium doping concentration in alloys or multilayers could therefore be increased significantly. More specifically, Zn- in a GaxIn1-xP multilayer is found to have a maximum solubility for x=0.9, which is 5 orders of magnitude larger than that of pure InP.