Measuring semantic similarity of web services has several benefits and most of the proposed service discovery algorithms are based on measuring the similarity of the requested service with each of the advertised services. In this paper, we propose a method for measuring the similarity of web services which are annotated with OWL-S ontology. First, a semantic similarity measure for determining the similarity of OWL concepts is discussed and then based on this measure, the functional similarity of services is defined. Then it is showed that the precision of algorithms that only take into account the functional properties of services for measuring their similarity are low. Therefore the textual descriptions of web services are also taken into account and the textual similarity of services is also calculated. Then it is showed how Neural Networks can be used for combining these two measures for a better compound measure. The proposed technique is applied to a sample test collection and experimental results are presented which demonstrate the effectiveness of the idea.