The major purpose of this thesis is to suggest a semantic categorization of English technical noun compounds, as well as to analyze the semantics and syntax of the Portuguese renderings. First, the literature on semantic relations in English compound nouns is reviewed. The classification here suggested is therefore based on classic studies on the semantics of compound nouns (Levi, 1978; Warren, 1978) and on more recent research within the scope of Computational Linguistics, which are influenced by the Generative Lexicon Theory (Pustejovsky, 1995). The semantic categorization is also adapted to the data collected in this work. This thesis also analyzes the Portuguese translation of the English compound nouns, as well as the role of the prepositions in prepositional phrases. The data was taken from an electrical/electronics engineering book which was translated by the author. In addition to the semantic classification, the technical compound nouns are grouped together according to the head or modifiers of the structure, and assembled into ontologies. Compound nouns sharing a common head or modifier are grouped together, so as to investigate if there is a hypernym-hyponym relation among the compounds assembled in the same ontology.