Developing high-performance chemiresistive gas sensors with high sensitivity and selectivity is challenging for various fields. In this work, a three dimensional (3D) framework of chemically reduced graphene oxide (RGO) was proposed for enhanced ammonia (NH₃) gas sensing performances via the combination of a 3D structural design and chemical functionalization techniques. SiO₂ spheres were used as templates for supporting the 3D graphene frameworks to enhance the sensitivity of sensing device through providing more reactive sites. Chemical modifications at room temperature were employed to further enhance the sensitivity and selectivity towards NH₃. Through this design, the resultant chemically reduced 3D SiO₂-RGO framework showed superior response (31.5%) towards 50 ppm NH₃ in 850 s to that of unmodified 2D plane-stacked RGO network sensor (1.5%). The oligomer layers formed in the reducing process were considered to be the key factor for enhanced performance through a doping/de-doping mechanism. As a result, its selectivity towards NH₃ was also greatly enhanced. The design of the chemically modified 3D SiO₂-RGO framework in this work can give an insight for high-performance RGO based sensors to detect different gases with suitable modifications.