This study explores coherence in research argument by investigating semantic overlaps in experts' and EFL students' texts. The semantic overlap is investigated through tracking the number of the recurrent concepts/terms, which form into lexical chains (LCs) in the macro- Theme and how these are resonated in the hyper-Themes. Macro- Themes are identified as the thesis statement in academic genre and hyper-Themes, the topic sentence of a paragraph. Both expert and student Introduction texts are quantitatively examined. The results reveal that the difference in semantic overlaps is not statistically significant between the experts' and novice writers' texts. Close analysis of the texts, however, reveals several weaknesses in the students' texts. First, they often resort to exact ＂repetition＂ when mentioning the key concepts, contrary to the experts who use other lexical cohesive devices to elaborate and explain difficult concepts. Second, the students often repeat static terms (e.g. ＂students＂) as opposed to abstract concepts, which prevents them from presenting in-depth argument. Third, they often cram the third move, occupying the niche, with numerous variables, producing very dense information at the end. Implications are drawn regarding raising student writers' awareness in deploying more effective LCs, macro- and hyper-Themes to sustain the key propositions in the argument.