An n-Fe2O3 film was grown on a n-Si substrate which had undergone surface treatment to form a double layer semiconductor electrode. The influence of the interface state on the electrode properties was studied. From photoluminescence measurements, we found that an interface state with high density of states exists lying above the top of the Fe2O3 valence band at 1.61 eV. The Fermi level is pinned by this interface state.Using energy band profiles, we give an explanation for the photoluminescence, as well as a theoretical calculation and analysis for the capacity-voltage curves and photo-current-voltage curves. These theoretical calculated curves agree well with the experimental data. This double layer semiconductor electrode with an interface state with high density of states is a promising material for solar cells of good stability and high photoelectric conversion efficiency.