Nanowire-nanocluster hybrid chemical sensors were realized by functionalizing gallium nitride (GaN) nanowires with titanium dioxide (TiO2) nanoclusters for selectively sensing benzene and other related aromatic compounds. Hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN nanowires followed by the deposition of TiO2 nanoclusters using RF magnetron sputtering. The sensor fabrication process employed all standard micro-fabrication techniques. X-ray diffraction and high resolution transmission electron microscopy confirmed the presence of anatase phase in TiO2 clusters after post-deposition anneal at 700 °C. A change of current was observed for these hybrid sensors when exposed to aromatic compounds such as benzene, toluene, ethylbenzene, xylene, and chlorobenzene mixed with air. However, these sensors did not show any sensitivity when exposed to methanol, ethanol, isopropanol, chloroform, acetone, and 1, 3-hexadiene. These sensors were capable of sensing the aromatic compounds only under ultraviolet excitation. The sensitivity range for all of the above mentioned aromatic compounds except chlorobenzene were from 1% down to 50 parts per billion (ppb) at room-temperature. By combining the enhanced catalytic properties of the TiO2 nanoclusters with the sensitive transduction capability of the nanowires, an ultra-sensitive and highly selective chemical sensing architecture is demonstrated. We have proposed a mechanism that could qualitatively explain the observed sensing behavior.