Although GPS that is a location determining system in high accuracy, has been developed for military purpose usage at the beginning, thanks to the developments in technology has found implementation possibility in daily life as well. When the GPS signals are transmitted from the GPS satellites to receivers in earth surface, they pass through the ionosphere. GPS signals, which play an important role in defining the position. GPS signals give some information in the ionosphere physics studies. They have not affected from the conditions when they were passing through the ionosphere layer. By using the signals which are coming from the GPS satellites, the regional and the global total electron amount can be estimated, electron density profiles can be derived, Total Electron Content (TEC) of ionosphere can be examined. Depending on the activity of the Sun, continuous changing at the electron density of ionosphere can cause delay of the GPS signals that passing through the ionosphere. In this study, by deriving benefit from GPS technique, the effects of ionosphere upon the GPS signals were researched; different ionosphere models were examined and, the changing of the electron density with altitude and TEC value were obtained by using IRI ionosphere model