Reflection spectra have been measured for Bi4Ge3O12 (BGO) crystals in the range from 4 to 40 eV, using synchrotron radiation. The reflection data are evaluated using a modified Kramers-Kronig method for extracting information on the optical constants. From the experimental spectra of the optical constants in a wide range and calculations of Xα-scattered waves of the molecular cluster an electron structure model for bismuth germanate crystals is suggested. The most interesting feature of our model is a dominant contribution of the bismuth state in the top of the valence band.