This research aimed to develop "Critical Thinking Skill Test for High School Students" to measure critical thinking (CT) skills of high school students. For the CT test prepared based on the sub-skills of inference, evaluating arguments, deduction, recognizing assumptions and interpretation which are deemed to represent CT (Watson and Glaser, 1994), content validity and face validity were achieved with expert opinions and the table of specifications. Following the item difficulty and item discrimination analyses performed to test the construct validity, 34 items were omitted from the test which was finalized with 51 items. While mean item difficulty values of the sub-tests vary between 0.51 and 0.63, mean item discrimination values range from 0.35 to 0.49. The total test has a mean item difficulty value of 0.52 and a mean item discrimination value of 0.42. Decision-making skill was used to test the criterion-related validity of the test. KR20 reliability coefficients calculated for the sub-tests ranged from 0.62 to 0.75. A KR20 reliability coefficient of the total test was 0.87. Moreover, a correlation coefficient of 0.84 was calculated with the split-half method. To test time invariance of the test, the correlation values calculated between the results of the two applications which were performed three months apart ranged from 0.57 to 0.70. The correlation coefficient for the total test is 0.70. Based on the results of validity and reliability studies, it can be said that the CT test will yield valid and reliable results in measuring CT skills of high school students.