A semi-passive fuel cell system is provided. A stack in which a plurality of unit cells are laterally stacked with one another is provided. Each unit cell includes a membrane-electrode assembly and bipolar plates located on both sides of the membrane-electrode assembly. The membrane-electrode assembly includes an electrolyte membrane, a cathode electrode, and an anode electrode. The cathode and anode electrodes, respectively, are formed on each side of the electrolyte membrane. Also provided are a means for supplying fuel and a means for supplying air. Each of the bipolar plates has air paths formed on a surface facing the cathode electrode and extending from an upper end to a lower end of the bipolar plate. The air supply means includes ducts which are respectively installed on an upper end and a lower end of the stack, and includes a means for blowing air through the ducts.