Different size crystal-like Nickel Oxide (NiO) on silicon Si (111) substrates were electrochemically deposited. The deposition time with constant applied current greatly affected the shape and size of the crystal, thereby altering its structural and optical properties. The crystal like of the fabricated nanostructures revealed NiO structures with different density of crystals and energy gap. We report the fabrication of metal–semiconductor–metal (MSM) photodetector (Al/NiO nanocrystals/Al) via a facile and simple processing method. Highly dense NiO nanocrystals were grown on Si (111) substrate via a two-step process; electrochemical deposition of Ni ions followed by oxidization of these samples in a furnace under ambient oxygen. The morphological, structural and optical properties of the produced nanocrystals have been investigated using field emission scanning electron microscopy, X-ray diffraction and spectrophotometer techniques. The grown nanocrystals were used in the fabrication of a MSM photodetector with Al contact electrodes. The results showed that, the contrast ratio (Ip/Id) increased after illuminating the fabricated devices resulting in higher photocurrents related to crystal size and density. The detector shows fast photoresponse with a rise time of 0.49 s and decay time of 0.56 s.