Plasma spray is a fast and inexpensive process for fabricating high performance yttria stabilized zirconia (YSZ) electrolyte for solid oxide fuel cells. In this paper, free-standing electrolyte disks consisting of YSZ with a diameter of 13 mm are produced by means of plasma spraying. The YSZ electrolyte disks are subjected to post-heat treatment at 1200, 1400, and 1500 deg C with holding times of 3 and 9 minutes with the help of a single and multi-cycle sintering process (Spark Plasma Sintering, SPS). The microstructure of the original and the post-treated electrolyte disks is examined by means of SEM. The mechanical properties and thermal conductivity of the electrolytes are measured to determine the effect of sintering. The results show that an SPS aftertreatment converts the lamellar structure of the plasma-sprayed panes into a coaxial granulated structure. The thermal conductivity of the electrolytes is significantly improved after SPS treatment. Paper includes a German-language abstract.