Ultrathin 3 mol.% yttria-stabilised-tetragonal-zirconia-polycrystal (Y-TZP) foils with thicknesses of 1-10 mu m are fabricated by a new wet-chemical processing route. The foils are free-standing, semi-transparent and flexible. The in-plane electrical conductivity of the Y-TZP foil is 0.03 S m(-1) at 500 degrees C. Cross-plane impedance measurements with sputtered Pt electrodes yield two arcs, of which the high-frequency arc is attributed to the ohmic resistance of the electrolyte and the low-frequency arc to the electrode-electrolyte interface. A symmetrical micro-solid oxide fuel cell (SOFC) is designed using this ultrathin free-standing Y-TZP foil as the electrolyte and sputtered Pt electrodes. An open-circuit voltage of 0.98V and a maximum power density of 12 mW cm(-2) are measured at 500 degrees C. These results prove the feasibility of this approach to the fabrication of miniaturised planar SOFCs without the need for microfabrication. (C) 2011 Elsevier B.V. All rights reserved.