The efficiency of state-of-the-art solid oxide fuel cells can be improved by applying YSZ electrolyte layers with thicknesses reduced to a few micrometers. This will allow the operating temperature of reactors made of these SOFC’s to be lowered to 800 - 900 °C. The membrane-based thin electrolyte layer SOFC technology is therefore being developed. A ceramic membrane is deposited on and integrated with the supported porous cathode layer. A modified-CVD process combined with an Electrochemical Vapor Deposition (EVD) process is used to grow a (very) thin gas tight YSZ layer on this composite layer system. Preliminary experimental depositions on alumina substrates show the formation of a gas tight YSZ layer (thickness of a few microns) after 6 hours of deposition. thin YSZ electrolyte layer SOFC technology. We aim to present a technology to reduce the layer thickness of the pre sently applied YSZ electrolyte layers to thicknesses of a few microns or less. This will decrease the ohmic polarization losses. Such a considerable reduction of the electrolyte layer thickness will allow the SOFC reactors to be operated at lower temperatures (800-900 °C). These (very) thin electrolyte layers require to be supported when produced. A suita ble production technique for thin supported YSZ layers is Electrochemical Vapor Deposi Mathematical in the present a preliminary experimental investigation, the EVD experiments were concen trated on the deposition of YSZ layers on porous alumina substrate disks. The experiments were performed in a CVD/EVD apparatus. The main part of the apparatus is an alumina tube reactor heated by a six zone furnace. All the experimental conditions such as reaction zone temperature, gas delivery and system pressure could be controlled in this apparatus. Typical experimental conditions were: total concentration of metal chloride vapor = 2.0xl0"9 mol/ml; YCl3/ZrCl4 ratio in vapor phase = 1:5 ; total pressure in reaction zone = 1.5 mbar; total water vapor concentration = 3.5xl0'9 mol/ml and the deposition temperature = 1000 °C. The two substrates used were porous alumina disks with mean pore sizes of 11.0 and 0.16 /xm, respectively. The deposition results were characterized by XRD, SEM and EDS. kinetics, the deposition of the solid electrolyte layer by the EVD process will be optimized.