This study analyzed the lexical devices used by undergraduate students in their argumentative text using Halliday and Hasan (1976) and Halliday's (2004) taxonomy. One hundred forty-eight argumentative essays were analyzed. The essays underwent interrating by three independent raters using a 20-point rubric and were grouped according to rating. Repetition was the most frequently used lexical cohesive device among the three groups of essays. Antonyms, meronyms, and hyponyms followed respectively. Super ordinates and collocation occurred less frequently in the essays. There was a low correlation between the frequency of lexical devices and writing quality. Therefore, there was no significant relationship between lexical cohesive devices and writing quality. Qualitative findings reveal that synonyms in the highly-rated essays were utilized by the students to denote the positive effects and to define technology. Antonyms were used for comparison and contrast and to denote the positive effects of technology in the low-rated essays. Unlike in the highly-rated essays where synonyms were used to give positive effects of technology, antonyms were used to denote positive effects of technology in the low-rated essays to achieve such communicative purpose. Other lexical devices assisted the students in fulfilling their writing requirement. Hyponyms were employed to explain how a particular concept contributes to or is a part of a bigger concept. Meronyms were used to give examples of a concept and to define a term. Superordinates were utilized to give a specific kind or brand of a more general idea.