Many electron density profiles of the dayside ionosphere of Venus have been measured by the Pioneer Venus orbiter between December 1978 and October 1980, using the dual-frequency radio occulation technique. The peak electron density as a function of solar zenith angle can be described by a simple Chapman layer theory with proper normalization; however, it does not predict adequately the height variation of the electron density peak. In order to interpret these radio occulations results, we have constructed a theoretical model describing the ion composition and electron density in the vicinity of the ionospheric peak. Good agreement between the model and the measurements were obtained only with a specific choice of the neutral densities, the electron temperature, and the level of solar activity.