In this study, heterojunctions of carbon nanotubes (CNTs) and tin oxide nanowires (SnO2) were investigated to determine their electrical performance for gas sensing applications. The I–V characteristics of the heterojunction were measured in air and H2S gas. The electrical parameters such as barrier height ϕB, ideality factor n, series resistance Rs, and reverse saturation current Io were extracted from the I-V plots. In H2S gas, the barrier height ϕB and series resistance Rs are lower compared to air, whereas the ideality factor n and saturation current Io are higher. These findings are essential for promoting technologies aimed at forming high-quality heterojunctions for gas sensing applications.