The aim of this study is to develop a valid and reliable measurement tool that measures critical thinking skills of university students. Pamukkale Critical Thinking Skills Scale was developed as two separate forms; multiple choice and open-ended. The validity and reliability studies of the multiple-choice form were constructed on two different theoretical frameworks as classical test theory and item-response theory. According to classical test theory, exploratory and confirmatory factor analyses were performed, to item-response theory, the Generalized Partial Credit Model (GPCM) for one-dimensional and multi-category scales was tested for the construct validity of the multiple-choice form of the scale. Analysis results supported the unidimensional structure of the scale. The reliability analyzes showed that the internal consistency coefficient of the scale and the item-total correlation values were high enough. The test-retest analysis results supported that the scale shows stability over time regarding the field it measures. The results of the item-response theory-based analysis also showed that the scale met the item-model fit assumptions. In the evaluation of the open-ended form of the scale, a rubric was used. Several studies were conducted on the validity and reliability of the open-ended form, and the results of the analysis provided psychometric support for the validity and reliability. As a result, Pamukkale Critical Thinking Skills Scale, which was developed in two forms, is a valid and reliable measurement tool to measure critical thinking skills of university students. The findings were discussed in the light of the literature and some suggestions were given.