Abstract: In this research, Manganese Sulfide (MnS) thin films were deposited by thermal evaporation technique on glass or silicon substrates. The structural and morphological characteristics of these films were introduced. They also showed good transparency in the spectral range 300-900 nm. The MnS/Si heterojunctions were successfully fabricated at different temperatures and their electrical characteristics were determined and found to be very dependent on the structure of MnS films. The optoelectronic characteristics of these heterojunction photodiodes were also determined. Maximum spectral responsivity of 0.165 A/W was measured at 450 nm while maximum detectivity was about 2.359×1012 cm Hz–1/2W–1 at 450 nm. This research is good attempt to fabricate MnS/Si heterojunction detectors with relatively good characteristics and low production cost.