ABSTRACT
This study aims to analyze the source language in third language acquisition (TLA) on Indonesian language acquisition for Bahasa Indonesia Bagi Penutur Asing (BIPA) students. The subjects of this study were BIPA Unesa students with the same study period but different language backgrounds. The data collection technique used is the elicitation technique. The lexical transfer is used as an aspect in determining the source language in the TLA. The results of this study show that the source of the language in Indonesian acquisition as L3 can be determined from three factors, namely, language distance, recency, and L3 language background proficiency. The closer the L1/L2 typology is to L3, the higher the probability of becoming a source language. The higher the proficiency level at L1/L2 in L3 acquisition, the higher the probability of becoming a source language. The L2 proficiency by L3 learners will have a high potential for being used as a source language in L3 acquisition.
