The development of high-performing sensing materials, able to detect ppb-trace concentrations of volatile organic compounds at low temperatures, is required for the development of next-generation miniaturized wireless sensors. Here, we present the engineering of selective room-temperature chemical sensors, comprising of highly porous tin dioxide (SnO2) – graphene ox-ide (GO) nano-heterojunction layouts. The optoelectronic and chemical properties of these highly porous (> 90%) p-n hetero-junctions were systematically investigated in terms of composition and morphologies. Optimized SnO2-GO layouts demon-strate significant potential as both visible-blind photodetectors and as selective room-temperature chemical sensors. Notably, a low GO content results in an excellent UV light responsivity (400 A W-1), with short rise and decay times, and room-temperature high chemical sensitivity with selective detection of volatile organic compounds such as ethanol down to 100 ppb. In contrast, a high concentration of GO drastically decreases the room-temperature response to ethanol, and results in good selectivity to ethylbenzene. The feasibility of tuning the chemical selectivity of the sensor response by engineering the relative amount of GO and SnO2 is a promising feature that may guide the future development of miniaturized solid-state gas sensors. Furthermore, the excellent optoelectronic properties of these SnO2-GO nano-heterojunctions may find applications to various other areas such as optoelectronic devices and (photo)electrocatalysis.