The main purpose of this paper is to present an analysis of scientific English register from a semantic perspective. Essentially, the author makes use of specific vocabulary belonging to the field of technical languages in order to explain how people working in specialized areas need to create technical terms to designate the new advances of every science, a task that is carried out with great objectivity, accuracy, clearness and preciseness, as the author points out. In order to exemplify the change of meaning that vocabulary in these areas has undergone, the author mentions specialization as one of the several options that specialists consider when dealing with technical terms (for example, "computer", "cursor" and "printer"). Generalization is regarded in cases where a specific word is given more general meaning (e.g. "interpolation" and "minimum"). Figurative language relates to the expansion of meaning through metaphorical elements (e.g. "friction", "network", "data", "eye", "foot"). Analogy or similarity refers to those nouns with a number of acquired senses (e.g. "spider"). Polysemy concerns words with more than one sense (e.g. "current", "energy", "exit" and "input"). Complete synonyms arise from classical and French loanwords (e.g. "burn-combustion", "fire-flame-conflagration", "input-entry", "output-exit", "memory-store"). Antonyms are classified into grammatical antonyms (e.g. "to activate-to deactivate") and lexical antonyms (e.g. "hard (disk)- floppy (disk)". Finally, pure lexical terms are adopted from other specialized areas (e.g. "navigation", "palette", "modem"). (Elena Ruiz Gil and Francisco Ruiz de Mendoza)