One of the issues of Artificial Intelligence is the transfer of the knowledge conveyed by Natural Language into formalisms that a computer can interpret. In the Natural Language Processing department of the IBM France Paris Scientific Center, we are developing and evaluating a system prototype whose purpose is to build a semantic representation of written French texts in a rigorous formal model (the Conceptual Graph model, introduced by J.F Sowa [10]). The semantic representation of texts may then be used in various applications, such as intelligent information retrieval. The accuracy of the semantic representation is therefore crucial in order to obtain valid resuits in any subsequent applications, in this article we explain how ambiguities related to Natural Language may be solved by semantic analysis using the Conceptual Graph model. Key words Natural Language Understanding, Computational Linguistics, Conceptual Graph Model. almost completely solved by the syntactic analyzer.