Communication science has been described as a fragmented field split into many distinct sub-domains that show little connections between each other. Although several studies have sought to determine the core topics of communication science, not much is known about the actual thematic commonalities among different sub-domains. Consequently, this study explores the knowledge structure underlying communication science to identify structural commonalities and important topics across its different sub-domains. A semantic network analysis based on the keywords of peer-reviewed articles published from 2008 to 2019 in communication journals focusing on different thematic areas is conducted. It was found that although the different journals show significant thematical overlaps with each other, the thematic core structure shared by all sub-domains consists of only a few keywords, implying a common core of communication science that consists of vaguely defined concepts open for interpretations.