In this paper a study about the application of the radioisotope XRF technique for coating thickness measurements in the field of light metal industry has been worked out. A large series of measurements has been carried out on standard steel samples with copper, zinc and lead coatings in a thickness range widely employed. The results obtained, by using a semiconductor detector coupled with an excitation line source, seem to be quite interesting from industrial and scientific point of view for the sensitivity and the accuracy shown.