Phase differences between the two carrier waves from Global Positioning System (GPS) sat ellites provide information on numbers of electrons integrated along line-of-sights. Sudden increase of electron densities in ionosphere is caused by enhanced ultraviolet flux by solar flares. Here I report two examples of such observations using globally deployed GPS stations. Dependence of such increase on solar zenith angles is addressed using stations distributed over the sunlit hemisphere. The height distribution of the electron increase is also discussed using data from stations along the night-day boundary.