Cupric oxide(CuO) is considered to be a promising material for photovoltaic applications. In this paper, p-CuO/n-Si junction solar cells were obtained by thermal oxidation of metallic copper films deposited on n-Si substrates at 400℃for 5 h. X-ray diffraction patterns show that the as-prepared films are CuO with monoclinic crystalline structure. Hall effect measurement results show that CuO films are p-type conduction. A direct band-gap of ~1.57 eV for the CuO film is deduced from UV-Vis absorbance spectra. Solar cells of Cu/p-CuO/n-Si/Al structure show that its photovoltaic behavior has a much wider spectrum response width compared with that of Si solar cells. In addition, the photocurrent of CuO/n-Si junction is investigated as a function of CuO film thickness, and it is found that the critical thickness for CuO on Si is about 250 nm.