Single phase Ca5Si3 and Sr5Si3 powders were prepared, and their electric and thermoelectric properties were investigated. The Ca5Si3 and Sr5Si3 powders are synthesized by exposure of the Si powders to Ca and Sr fluxes, respectively. It is found that both silicides show a p-type conduction and semiconductor-like behavior. The electronic band structures of the silicides are calculated using the first-principles total-energy calculation program in pseudopotential schemes with plane-wave basis functions. The calculated result predicts the possibility of a semiconductor-like property with a sharp pseudogap at the Fermi level for Ca5Si3, as experimentally obtained. The silicide would be expected to be a new semiconductor-like conducting material. (c) 2007 Elsevier B.V. All rights reserved.