Photoemission spectra (XPS and UPS) of As-covered Si (001) surfaces prepared at high (>600ºC) and low (<450ºC) temperatures and GaAs epilayers subsequently grown on them were measured without exposing to air. It was found that the surface electronic structures of As/Si prepared at the low temperature are different from those of the high temperature sample, the spectra of which can be interpreted as a symmetric dimer model. Differences were also observed between the GaAs epilayers on the As—covered Si surfaces prepared at the high and low temperatures. The temperature dependence of the surface and interface structures are discussed.