This study examined whether processing ambiguous sentences containing relative clauses (RCs) following a complex determiner phrase (DP) by Persian-speaking learners of L2 English with different proficiency and working memory capacities (WMCs) is affected by semantic priming. The semantic relationship studied was one between the subject/verb of the main clause and one of the DPs in the complex DP to see if, as predicted by Spreading Activation Model, priming one of the DPs affects the L2 learners’ preference. The results of a task using Rapid Serial Visual Processing showed that semantic priming does not affect the choice of the antecedent; rather, the L2 learners' processing is guided by syntactic information. A negative correlation was found between WMC and RC attachment preferences. The findings support the predictions of the chunking hypothesis for L2 learners.