Chemical thinking is widely acknowledged as a core competency that students should develop in the context of school chemistry. This study aims to develop a measurement instrument to assess students' chemical thinking. We employed the Essential Questions-Perspectives (EQ-P) framework and Structure of Observed Learning Outcome (SOLO) classification to construct a hypothetical model of chemical thinking. This model comprises three aspects and each aspect includes five cognitive levels to assess students' chemical thinking. Accordingly, we developed an initial instrument consisting of 27 items in multiple formats, including multiple-choice, two-tier diagnostic, and open-ended questions. We applied the partial credit Rasch model to establish the validity and reliability of measures for the final instrument. Following the process of pilot test, revision, and field test, we finalized the instrument with a refined 20-item instrument. Two hundred and twenty-one Chinese high school students (Grade 12) participated in the pilot and field tests. The results demonstrate that the final instrument effectively produces reliable and valid measures of students' chemical thinking. Furthermore, the empirical results align well with the hypothetical model, suggesting that the SOLO classification can effectively distinguish the levels of proficiency in students' chemical thinking.