Abstract
Saudi students face many challenges when studying in English at university level. Some of these challenges are caused by inadequate English-language proficiency. Since knowledge of vocabulary plays an important role in language proficiency, increasing one’s English vocabulary can lead to improved academic performance. Technology can help students improve their English vocabulary and consequently their language proficiency. Mobile applications have been used in the classroom; research has shown that they have a positive impact on language proficiency. However, few research studies have examined whether the use of mobile applications can improve vocabulary depth or breadth among Saudi university students. The present study investigates the effect of a mobile application, Vocabulary.com, on the vocabulary depth and breadth of 143 Saudi female university students at a university in Riyadh. Pre- and posttests of vocabulary depth and breadth were administered to control and experimental groups. The data were analyzed using descriptive statistics and both parametric and non-parametric statistical tests. The results show statistically significant differences in the post-test results of the control and experimental groups, with the latter performing better. These findings indicate that mobile applications can have a positive impact on vocabulary breadth and depth among Saudi university students.

Key words: Keywords: vocabulary breadth, vocabulary depth, MALL, CALL, Vocabulary.com