By the nuclear method perturbed angular correlations (PAC) the microscopic structure of different types of ternary chalcopyrite semiconductors is investigated. It is shown with some examples that the annealing of radiation damage, the dynamics of defects, phase transitions and some details of phase diagrams can be studied by this method. The position of the radioactive atoms in the substances investigated is determined and the structure and temperature dependence of the electric field gradients at the probe sites is analysed by experiment as well as theoretically.