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Nano porous structure has been prepared on p - type Silicon wafer by anodic electrochemical etching process. An n -type SnO2 thin film of thickness 500 nm has been coated over the Porous Silicon (PS) layer, using spray pyrolysis technique. Photoluminescence studies of the PS show emission peak between 700 and 702 nm for the constant excitation at 365 nm. All the porous silicon structure emits bright red tight, as the prolonged etching with HF increases the porosity and thus produces smaller columnar structures. The dark I-V characteristics of SnO2/PS hetero-junction at different operating temperatures, indicates rectifying properties. Sensing properties of the SnO2/PS structure towards LPG and CO gas have been investigated in a specially designed sensor test rig. The dynamic characteristics studies of the device show two fold and one fold increase in current, after its exposure to LPG and CO gas respectively. Maximum sensitivity of the device has been found to be 42% and 29% for LPG and CO gas respectively, at the optimum operating temperature 450 °C. The response time has been estimated as 295 sec. and 410 sec., for LPG and CO gas respectively. Studies indicate that high sensitivity and short response time of the SnO2 / PS structure makes it attractive for gas sensing applications. [ABSTRACT FROM AUTHOR]