This study investigated the relationship between working memory (WM), semantic-encoding (SE) ability, and reading comprehension (RC) within the domain of second language acquisition (L2). 120 L1-Persian EFL learners were placed in three proficiency groups (beginning, intermediate, and advanced) based on their scores on the IELTS test. The participants engaged in a battery of cognitive tasks, including a reading span task, two semantic encoding (SE) tasks (sentence verification task and lexical access task), an L1-recall task, and a reading test. The scores and reaction times obtained from these measures were analyzed using a one-way ANOVA, a correlational analysis, and single regression analyses. The findings revealed significant differences in reading performance and semantic encoding skills across proficiency groups, with large effect sizes. Correlational analyses indicated a significant positive relationship between WM and RC, specifically in the beginner group. Moreover, WM was shown to correlate with the speed of SE in the beginner group, but not with its accuracy. Notably, SE speed correlated with RC performance, particularly under time-constrained conditions at lower proficiency levels. In the intermediate and advanced groups, working memory (WM) showed no correlation with reading comprehension (RC) or semantic encoding (SE). Conversely, both WM and SE speed were identified as strong predictors of L2 reading performance among learners with lower English proficiency. However, the study is not without its limitations, including a relatively small sample size, the absence of qualitative measures, and the potential influence of unassessed reading subskills such as grammar and vocabulary.