More than 1.4 million S4-index profiles sounded by FORMOSAT-3/COSMIC (F3/C) radio occultation during 2007-2014 are used to construct a global scintillation occurrence model for the ground-based GNSS (Global Navigation Satellite System) users. The local maximums of each F3/C S4-index profile at every 10 km altitude window are integrated to simulate the worst-case L-band S4-index (S4conv) on the ground. The S4conv mega-data bind into 3˚×3˚ in latitude×longitude allows us computing the occurrence probability of the globe for a given S4-index threshold. The occurrence probability of S4 of the developed model agree well with those of ground-based GNSS receivers of the SCINDA (SCIntillation Network Decision Aid) network. Global patterns in the occurrence probability of the model are similar to that of in-situ plasma measurements probed by ROCSAT and FORMOSAT-7/COSMIC-2 satellites in various solar activities. These agreements and similarities indicate that the constructed empirical model can be employed to calculate and predict L-band S4-index and its occurrence probability in the ionosphere.