A single solid oxide fuel cell (SOFC) with a La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM) electrolyte 200 mu m thick with H-2 as fuel gave 1.4 W/cm(2) peak power density at 800 degrees C. With a La0.4Ce0.6O1.8 (LDC) buffer layer 20 mu m thick between the electrolyte and the two electrodes, a 30- day test showed essentially no degradation of the output power. The tests demonstrated the feasibility of an SOFC operating at temperatures T < 800 degrees C with LSGM as the electrolyte. Moreover, an LSGM electrolyte 200 mu m thick with 20 mu m LDC buffer layers on either side offers a convenient test bed for the exploration of new electrode materials. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1943587] All rights reserved.