Finding semantic similarity is an important task in many natural language processing applications. Despite numerous works for popular languages, there is still limited research done for Vietnamese. In this paper, we tackle the problem of finding semantic similarity for Vietnamese using Random Indexing and Hyperspace Analogue to Language to represent the semantics of words and documents. We build a system to find synonyms in Vietnamese. Experimental results show that our system achieves accuracies of 75% for finding synonyms for verbs and 65% for synonyms for nouns.