In this research, a highly sensitive and selective hydrogen gas sensor was developed based on Cu-doped SnO2. Sensing characteristics were compared based on SnO2 doped with different concentrations of Cu, and the highest sensitivity and fastest response time were shown when 3% Cu was contained. A 3D structure was formed using a polystyrene to increase the surface-to-volume ratio, which allows more oxygen molecules to bond with the surface of the SnO2 sensing material. Extremely increased sensitivity was observed as compared to the planar structure. A temperature sensor and micro-heater were integrated into the sensor, and the surface temperature was maintained constant regardless of external influences. In addition, an electronic sensor interface was developed for the efficient analysis of real-time data. The developed sensor was wire-bonded to the flexible printed circuit board (FPCB) cable and connected with the sensor interface. Sensitivity and linearity measured based on the developed sensor and interface system were analyzed as 0.286%/ppm and 0.98, respectively, which were almost similar to the results observed by a digital multimeter (DMM). This indicates that our developed sensor system can be a very promising candidate for real-time measurement and can be applied in various fields. The enhanced sensitivity of 3% doped SnO2 toward hydrogen is attributed to the huge number of oxygen vacancies in the doped sample.