Cobalt sulfide (CoS) thin films were deposited on glass substrates using a modified chemical bath deposition with cobalt dichloride (CoCl2) and sodium sulfide (Na2S) aqueous solutions. Structure properties of the films were measured using X-ray diffraction and scanning electron microscopy in the as-deposited and annealed states. Band gaps were determined using optical absorption measurements and carrier transport properties using conductivity measurements. The result shows that thermal annealing promotes the growth of grains, decreases band gap, and enhances electrical conductivity. The conductivity activation energy measurements show that the Fermi level always stays at the middle of the band gap for both as-deposited and annealed states, indicating an intrinsic semiconductor that may be suitable for photovoltaic or photothermal applications.