Tin-doped cadmium oxide (Sn:CdO) transparent thin films with different Sn concentrations were deposited on glass and p-silicon substrates by the chemical spray method at 250 °C. Different concentrations of stannic chloride were used to prepare Sn:CdO thin films. The prepared doped and un-doped CdO films were subjected to X-ray diffraction (XRD), scanning electron microscopy and atomic force microscopy, optical absorption, and electrical analyses to characterize their structural, morphological, optical, and electrical properties, respectively. XRD analysis demonstrated the growth of polycrystalline and cubic CdO with preferential orientation along the (111) plane. Sn-doping shifted the XRD peaks slightly towards a higher Bragg angle and increased the band gap of CdO thin films. Variation in doping concentration also affected the morphology of the films. Optimum Sn-doping increased the electrical conductivity of CdO thin films. Furthermore, to the best of our knowledge, the photoresponse analyses of the fabricated un-doped and doped n-CdO/p-Si heterostructures were performed for the first time in this study.