Although the development of critical thinking (CT) is a major goal of science education, adequate emphasis has not been given to the measurement of CT skills in specific science domains such as physics. Recognizing that adequately assessing CT implies the assessment of both domain-specific and domain-general CT skills, this study reports on the development and validation of a test designed to measure students' acquisition of CT skills in electricity and magnetism (CTEM). The CTEM items were designed to mirror the structural components of items identified in an existing standardized domain-general CT test, and targeted content from an introductory Electricity and Magnetism (E&M) course. A preliminary version of the CTEM test was initially piloted on three groups of samples: interviews with physics experts (N = 3), student cognitive interviews (N = 6), and small-scale paper and pencil administration (N = 19). Modifications were made afterwards and the test was administered to a different group of second-year students whose major was mechanical engineering (N = 45). The results showed that the internal consistency (Cronbach's a = 0.72) and inter-rater reliability (Cohen's kappa = 0.83) of the CTEM test are acceptable. The findings overall suggest that the CTEM test can be used to measure the acquisition of domain-specific CT skills in E&M, and a good basis for future empirical research that focuses on the integration of CT skills within specific subject matter instruction. A broader CT assessment framework is proposed and possible research questions that can be addressed through the CTEM test are discussed.