ABSTRACT: Tin oxide (SnO/SnO₂) thin films with an average thickness of about 400 nm were fabricated on glass substrates using physical vapor deposition (PVD). To assess the effect of thermal treatment, the deposited films were subsequently annealed at 200 °C and 300 °C. X-ray diffraction (XRD) measurements revealed the simultaneous presence of tetragonal SnO and orthorhombic SnO₂ phases in all specimens. After annealing, the diffraction peaks became more intense and narrower, reflecting enhanced crystallinity and grain development. Atomic force microscopy (AFM) showed a marked reduction in root-mean-square (RMS) surface roughness from approximately 9.7 nm in the as-deposited state to about 6.3 nm at 200 °C and 5.4 nm at 300 °C, accompanied by an increase in mean grain size from roughly 49 nm to 67 nm and 62 nm, respectively. UV–visible spectroscopy indicated high optical transparency (>75%) throughout the visible spectrum along with a slight blue shift of the absorption edge. The optical band gap shifted from 2.8 eV (unannealed) to 2.9 eV at 200 °C and remained close to 2.8 eV after annealing at 300 °C. Collectively, these findings confirm that post-deposition annealing improves the crystallinity, surface smoothness, and optoelectronic performance of SnO/SnO₂ thin films, thereby enhancing their suitability for transparent electrodes, optoelectronic components, and gas-sensing applications