The role of the impurity donor band in the conductivity of the heavily doped and compensated intermetallic TiCoSb semiconductor is determined. The electronic structure of the TiCo_1-x Ni_xSb semiconductor alloy is calculated. A model of impurity band transformation in the TiCoSb semiconductor due to donor impurity doping is suggested. The transition from activated to metallic conductivity when varying the TiCo_1-x Ni _xSb alloy composition is detected, which we identify with the Anderson transition.