To improve the surface quality for photovoltaic applications, we have investigated the effects of post-annealing on the surface structure and carrier lifetime of evaporated BaSi 2 films. Structural characterizations by Raman spectroscopy and X-ray diffraction analysis show that there is an optimum post-annealing duration for fabricating a homogeneous film up to around the surface. By detailed surface analysis by X-ray photoelectron spectroscopy, the existence of a surface oxidation layer consisting of BaCO 3 and barium silicate is revealed, and the thickness of the oxidation layer is found to be smallest for the optimum post-annealing duration. These surface structural changes are discussed from a thermodynamic viewpoint. Carrier lifetime is also investigated by the microwave-detected photoconductivity decay method, which shows that the structural change around the surface by post-annealing has negligible effects on carrier lifetime, possibly because the silicate layer covers the BaSi 2 surface irrespective of post-annealing duration.