This study aimed at developing the Silpakorn Test of English Proficiency (STEP), in alignment with the Common European Framework of Reference for Languages (CEFR), and in accordance with the theoretical framework established by Alderson et al. (2006). Four major steps were involved in the test construction. First, English language lecturers who served as content specialists were asked to design can-do statements presented in the CEFR. Then the specialists designed the test specification based on the can-do statements. Four skill areas: listening, semi-speaking, reading, and semi-writing were targeted as the test construct. At this juncture, the content specialists were required to write test items in accordance with the test specification. Next, the test items constructed were determined for their validity and reliability. Finally, a standard setting was carried out. The results demonstrated that the framework offered by Alderson et al. (2006) served as an effective reference document for developing the STEP. In terms of validity and reliability, the STEP was of statistical significance, that is, it could be aligned with the CEFR levels and measure test takers' English proficiency at a specific CEFR level. The current findings provide useful insights for test developers or researchers who wish to design proficiency tests in alignment with the CEFR.