Abstract This quasi-experimental study investigated the effect of using semantic mapping as instructional strategy on foundation students' vocabulary development. It also explored the students' attitudes towards using the strategy of semantic mapping on learning vocabulary. The study answered the following research questions: 1.Is there a significant difference between students who were taught vocabulary using semantic mapping instructional strategy and the students who were taught vocabulary using the conventional approaches to teaching vocabulary on their vocabulary development? 2.What are the students' attitudes towards using semantic mapping strategy in learning vocabulary? The sample of the study included four intact classes of level six students from the pool of foundation students at Sultan Qaboos University, Center for Preparatory Studies during summer school period in the academic year 2017/2018. Two classes were assigned as an experimental group and other two classes were assigned as a control group. The total sample was 41 students. The instruments of the study were a vocabulary tests (pre- test and post-test) and an attitude questionnaire. Data analysis revealed the following: 1. There was no significant difference between students who were taught vocabulary using semantic mapping and those who were taught vocabulary using the conventional methods of teaching on their vocabulary development. 2. Students have highly positive attitudes towards semantic mapping strategy in learning vocabulary.