The Feeling of Familiarity (FOF) is a metacognitive judgment whose activation occurs when perceiving a stimulus coming from the environment, in the current research is presented the formal and semantic representation of a FOF in metacognitive architecture CARINA. A FOF is presented as a production rule, which has the following fields; condition, assert, strategy, next and else. Also, is presented the formal and semantic representation of a reasoning trace and the semantic representation of a belief in CARINA'S metacognitive architecture. Finally, the presentation and explanation of a software prototype (FOF software) created to test the process that seeks to create in CARINA for the activation of a metacognitive judgment, in this case Feeling Of Familiarity. Also, the results obtained from the tests carried out with this and the conclusions obtained in the realization of the current investigation are shown.