A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) lambda of the ionospheric pierce point (IPP) and the IEF's influence factor (IFF) (lambda) over bar The IEF can be used to make a relatively precise distinction between ionospheric daytime and night-time, whereas the IFF is advantageous for describing the IEF's variations with day, month, season and year, associated with seasonal variations of total electron content (TEC) of the ionosphere. By combining lambda and (lambda) over bar with the local time t of IPP, the IEFM has the ability to precisely distinguish between ionospheric daytime and nighttime, as well as efficiently combine them during different seasons or months over a year at the IPP. The IEFM-based ionospheric delay estimates are validated by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM may further improve ionospheric delay modeling using GPS data.