A process for producing metal oxide thin films on a substrate by the ALD method comprises the steps of bonding no more than about a molecular monolayer of a gaseous metal compound to a growth substrate, and converting the bonded metal compound to metal oxide. The bonded metal compound is converted to metal oxide by contacting it with a reactive vapor source of oxygen other than water, and the substrate is kept at a temperature of less than 190.degree. C. during the growth process. By means of the invention it is possible to produce films of good quality at low temperatures. The dielectric thin films having a dense structure can be used for passivating surfaces that do not endure high temperatures. Such surfaces include, for example, organic films in integrated circuits and polymer films such as in organic electroluminescent displays and organic solar cells. Further, when a water-free oxygen source is used, surfaces that are sensitive to water can be passivated.