The dependence of the electrical behavior of thin HfAlO x layers (5 nm) on post-deposition annealing temperature (T A ) has been studied at a nanometer scale using conductive atomic force microscopy (CAFM) and high resolution transmission electron microscopy (HR-TEM). Topography, current maps and current-voltage (I-V) characteristics have been collected by CAFM. Current maps show an increase in conduction inhomogeneity for samples exposed to T A >=900 o C: spots with current about one order of magnitude larger than the background region are present. The dielectric layer structure also becomes more inhomogeneous: HR-TEM images reveal that for T A >=900 o C HfO 2 grains appear on the HfAlO x layer, whereas for lower T A the HfAlO x layer is homogeneous. Moreover, for T A >=900 o C the high-k/Si interface becomes rougher. Therefore, the increase in conduction inhomogeneity for samples annealed above 800 o C is believed to be caused by the material transition from an amorphous to a poly(nano)crystalline structure combined with the increase of the high-k/SiO 2 interface roughness.