This paper describes the process of developing a screening test of English for specific academic purposes (ESAP) for science and engineering graduate students. Due to globalization, many graduate programs in Taiwan offer English medium instruction (EMI) as a way to attract international student enrollment. Along with the programs comes the special need to screen students' English proficiency level for admission. Currently no specialized screening tests are available for this purpose. The present paper describes the development of a vocabulary test to be used along with existing ESAP tests, and reports on analytical results which indicate its construct validity and correlation to the existing tests. The results of the study indicate that the newly constructed test is highly correlated to full-length ESAP standardized tests of reading and listening, both before and after students received intensive science and engineering ESAP instruction. In addition, the results of questionnaires indicate that the test was well received by test-takers. The test has proved to be reliable and valid, while economical in cost and test-taking time. Lessons learned from this study include an improved understanding of the design and implementation of the screening test in content-related vocabulary.