The properties of iron disilicide (FeSi2) have been investigated, and it has been shown to be a semiconductor with a thermal energy gap of 0.88 ± 0.04 eV.It has been found possible to dope FeSi2bothnandptype by the substitution of suitable elements for iron and silicon. The doping mechanism is obscure since relatively gross quantities (2–5%) of dope are required to achieve optimum thermoelectric properties. Substitution of cobalt for iron yields ann-type material, and substitution of aluminium for silicon produces ap-type material. These materials haveZ> 2 × 10−4deg C−1over the temperature range 150–650°C.The materials are oxidation-resistant, thermally stable and mechanically strong.A method of construction is described which exploits the properties of these materials and should produce a cheap, robust generator of high power/weight ratio.