Ontologies are in the heart of the knowledge management process. Different semantic measures have been proposed in the literature to evaluate the strength of the semantic link between two concepts or two groups of concepts from either two different ontologies (ontology alignment) or the same ontology. This article presents an off-context study of eight semantic measures based on an ontology restricted to subsomption links. We first present some common principles, and then propose a comparative study based on a set of semantic and theoretical criteria.