In this study, an InSe thin film layer was deposited onto a CdS thin film layer produced via the chemical bath deposition (CBD) method using the Successive Ionic Layer Adsorption and Reaction (SILAR) technique. The produced heterojunction devices were divided into two groups, and one group was annealed in an ambient atmosphere at 80°C for 1 hour. The electrical characterization of both heterojunction devices was performed in the dark and under an illumination intensity of 100 mW/cm². The fundamental diode parameters (n, ϕb, Rs, I0)were analyzed using different methods. Furthermore, key photodetector parameters such as photocurrent, photoresponsivity, photosensitivity, and specific detectivity were determined for these two devices.