Doped polysilicon layers are widely employed in fabricating thermal microsystems such as bolometers, micro hotplates or thermopiles thanks to their thermal and electrical properties. Since the performances of such devices are strongly influenced by heat conduction, a precise characterization of polysilicon thermal conductivity is of paramount importance. In order to determine the thermal conductivity (k) of thin films, microstructures like those proposed in [1] can be adopted. In this work, such microstructures have been adopted in order to investigate the dependence of polysilicon thermal conductivity on the type of doping adopted (p or n-type) and the annealing conditions.