Olfactory diagnosis presents a promising non-invasive approach to lifelong chronic disease monitoring. Metal oxide gas sensors without external heaters prove effective in meeting the requirements of miniaturization and low power consumption in smart healthcare. In this work, we designed a sensitivity-computable self-heating gas sensor featuring a suspended thin lines array structure made of SnO2 as the sensing element and Pt interdigitated electrodes. Experimental results showed the comparative advantages of gas sensitivity and the self-heating efficiency of the sensor over previous methods. The joule heating of sensors with various essential parameters, such as the width of the thin line, pairs of electrodes, and spacing between each line, were investigated numerically using COMSOL Multiphysics. With a 10 V DC bias voltage, the steady-state temperature of 283.35 °C was achieved on the surface of the sensing element. A higher surface-to-volume ratio of the thin lines array structure was found to decrease the maximum surface temperature of the designed SnO2 sell-heating gas sensor.