The addition of either Sm or Dy rare earth metal elements to Al thin films decreases markedly the grain size of the Al matrix and largely suppresses the growth of hillock and whisker thermal defects at high temperatures (350-450 degrees C). A large number of particles of fine metallic compounds of Al(3)RE (RE = Sm or Dy) were segregated in an Al matrix, mostly at grain boundaries, after annealing at 350 degrees C. The resistivities of the films after annealing at the above temperatures show very low values of less than about 50 n Omega m, without salient formation of hillocks or whiskers on the film surfaces.