The present study incorporates gas sensing mechanism for a chemi-resistive type sensor using semiconducting metal oxides (SMO) as sensing material. A detailed view of the interaction process between the target gases and sensor surface has been included with some vital examples of SMO sensor. Furthermore, the advantages and disadvantages of SMO sensor have also been discussed. To explore the sensing mechanism in a better way, different models and influencing factors in gas sensing are included and discussed. So, in this paper we report a focused study on the sensing mechanism of semiconducting metal oxides helpful to explore and correlate different sensing characteristics of the material.