Nickel hydroxide (Ni(OH)2) is a wide bandgap semiconductor with a bandgap energy of 3–3.5 eV, but the use of Ni(OH)2 as a semiconductor is still limited. In this study, Ni(OH)2 thin films were synthesized on indium tin oxide (ITO) coated glass substrates by electrochemical deposition and subsequent annealing in water vapor at 180°C. The as-deposited Ni(OH)2 films were amorphous α-Ni(OH)2 intercalated with water and nitrate molecules. Nanocrystallites of β-Ni(OH)2 were formed in the films during annealing in water vapor at 180 °C. The content of β-Ni(OH)2 nanocrystallites increased with increasing annealing time. The as-deposited and annealed Ni(OH)2 films exhibited an n-type photo response in photoelectrochemical measurements. The resistivity of the annealed films was about 1×104 Ωcm. This resistivity value was one order of magnitude lower than that of the as-deposited film. The Ni(OH)2/NiO/ITO heterostructure was fabricated by depositing Ni(OH)2 on nickel oxide (NiO). The n-Ni(OH)2/p-NiO/ITO heterostructure diode exhibited clear rectification behavior.