The role of the donor impurity band in the conduction of highly doped and compensated intermetallic semiconductors with MgAgAs type of structure was investigated. A simulation of the electronic structure for TiCo1−xNixSb semiconducting solid solution was carried out. A scheme of the impurity band transformation in TiCoSb semiconductor due to donor impurities doping was advanced. A conduction transition from activated to metallic type when the TiCo1−xNixSb solid solution composition changes was observed. This conduction transition is associated with the Anderson-type transition.