Transparent and conductive thin films consisting of p-type nickel oxide (NiO) semiconductors were prepared by r.f. magnetron sputtering. A resistivity of 1.4 x 10(-1) Ohm cm and a hole concentration of 1.3 x 10(19) cm(-3) were obtained for non-intentionally doped NiO films prepared at a substrate temperature of 200 degrees C in a pure oxygen sputtering gas. An average transmittance of about 40% in the visible range was obtained for a 110 nm thick NiO film. A semitransparent thin film pin diode consisting of p-NiO/i-NiO/i-ZnO/n-ZnO layers having a voltage-current rectification characteristic and an average transmittance above 20% in the visible range was fabricated on a glass substrate.