Electronic structures of Fe4Si4-nGen (n = 0-4) with a cubic B20-type structure are calculated by a self-consistent LMTO method. It is found that these compounds are narrow-gap semiconductors in the non-magnetic state. The band gap is found to decrease with increasing n. For n greater than or equal to 2, however, the metallic state with the magnetic moment of about 1mu(B) per Fe is shown to be more stable. It is also shown that the characteristic properties of itinerant-electron metamagnetism, i.e., the first-order transition at the Curie temperature and the field-induced metamagnetic transition, may take place at the boundary between the non-magnetic and magnetic states near n = 2. (C) 2003 Elsevier B.V. All rights reserved.