The mechanisms underlying native (L1) and non-native (L2) sentence processing have been widely debated. One account of potential L1/L2 differences is that L2 sentence processing underuses syntactic information and relies heavily on semantic and surface cues. Recently, an alternative account has been proposed, which argues that the source of L1/L2 differences lies in how susceptible L1 and L2 speakers are to interference during memory retrieval operations. The present study tested these two accounts by investigating filler-gap dependency formation and susceptibility to similarity-based interference in L1 and L2 language comprehension. The results demonstrated that L1 and L2 speakers recover the information of the filler upon encountering a gap and are susceptible to similarity-based interference during filler-gap dependency formation. However, there was no significant evidence of L1/L2 differences. These findings suggest that L1 and L2 speakers similarly engage in cue-based memory retrieval operations during filler-gap dependency formation.