When extending a UML metaclass with a stereotype, it is critical to ensure that the metaclass and the stereotype are semantically related. This is because a stereotype is a way to extend the UML metamodel to create new kinds of model elements that can include additional semantics and constraints, but still adhere to the base behavior defined by the metaclass. The stereotype should be a meaningful specialization of the metaclass and not contradict its fundamental semantics. By keeping them semantically related, there is less need for additional constraints on the metamodel, and the resulting profile is more intuitive for users. This is consistent with the principles described in the UML 2 Specification, particularly in the sections on profiles and stereotypes.