The aim of the present paper is examining the mental representations activated by semantic networks in media discourse. It studies the cognitive frames that are mentally constructed and activated about illegal immigrants, in general, and Syrian refugees in particular. Any word class can evoke frames, but to limit the scope of analysis, Fairclough's socio-cultural approach is implemented to work out the experiential, relational and expressive values of only nouns and adjectives in media discourse. The corpus consists of articles released by "The Guardian" newspaper during and after the Syrian refugee crisis between 2015 and 2019. The results of the research show that cognitive frames are used to enhance the stereotypical categorizations of refugees as dislocated, uprooted and oppressed communities. This paper focuses on the mental mapping of such disadvantaged people and how they are categorized and presented in media discourse. It also analyses nouns and adjectives as generators or builders of cognitive frames in the human mind via discourse. This study is original because it relates semantic networks, mental lexicon and cognitive frames to analyze media discourse.