The study aimed to analyze the content validation of the STEM-integrated on thermal and transport concept inventory instrument used to measure the problem-solving abilities of high school students. The instrument questions developed amounted to nine description questions. This type of study is development research. The steps in this research are define, design, development, and dissemination. However, in this study, it was limited to the design stage (expert validation). Furthermore, the instrument was assessed qualitatively and quantitatively by a validator consisting of three experts and five users. Assessment aspects include material, language, and construction. The qualitative data collected was analyzed qualitatively, and the quantitative data were analyzed using the Content Validity Ratio (CVR). The results showed that nine items had a CVR value exceeding 0.75, which meant that all items had valid criteria for content validity. The CVR value obtained is between 0.88 and 0.96, which means that the instrument has high criterion validity.