Reduced graphene oxide (rGO) is considered as one of the ideal sensing materials for high-performance room-temperature gas sensors owing to its large specific surface areas, numerous active sites, and high carrier mobility. However, the sensing performance cannot be maximized due to the inevitable sheet stacking and agglomeration. Herein, we firstdemonstrate multichannel room-temperature gas sensors using magnetic-field-induced alignment of three-dimensional (3D) Fe3O4@SiO2@rGO core-shell spheres. Moreover, the sensing channels composed of spheres can be tailored by changing the concentration of spheres and the magnetic field. Experimental results suggest that the multichannel 3D Fe3O4@SiO2@rGO sensor exhibits an ultrahigh sensitivity of 34.41 with a good response stability and high selectivity toward 5 ppm of NO2 at room temperature, which is ca. 7.96 times higher than that of the random 3D rGO gas sensor. The high performance can be mainly ascribed to a full utilization of their large specific surface area and active sites of rGO nanosheets. We believe that our results not only contribute to the development of high-performance rGO-based sensing devices, but also provide a general approach to maximize the sensing performance of other nanomaterials.