Lanthanum oxide and lanthanum aluminate thin films were deposited oil Si substrates. The as-grown films were stored in wet ambient and dry ambient for days and annealed after storage and also the structural and the electrical properties of the films were investigated. As the storage time increased, the La2O3 films stored in wet ambient showed rapid reaction with moisture and the properties degraded. In case of the LAO films, although the thickness of the film also increased during hydration, the properties of the film did not so much changed due to the role of the incorporated aluminium. The LAO films showed better hydration resistance characteristics and so more suitable for conventional wet cleaning process in semiconductor fabrication. (c) 2005 Elsevier B.V. All rights reserved.