Dense electrolyte thin film made of Ce0.8Gd0.2O1.90 (GDC20) with a thickness of about 10 run and supported by Ni-Gd0.1Ce0.9O1.95 (GDC) cermet anode was fabricated in situ by solid-state reaction of ceria and gadolinia. The open circuit voltage of this GDC20 cell is 0.86 V at 600 degreesC and 0.95 V at 500 degreesC. With La0.8Sr0.2Co0.2Fe0.8O3 (LSCF)-GDC composite cathode, we could achieve an excellent cell performance with the maximum power density of 578, 358, and 167 mW/cm(2) at 600, 550 and 500 degreesC, respectively, under open-air conditions. With airflow through the cathode, the maximum power density increases to 625 mW/cm(2) at 600 degreesC. It was also found that the cell impedance/polarization under open circuit is dominated by electrode polarization contribution; while under high cell overpotential, it is governed by both ohmic loss and electrode polarization contribution. (C) 2004 Elsevier B.V. All rights reserved.