The purpose of this research was to develop an instrument that can be used to measure higher-order thinking skills (HOTS) in mathematics instruction of high school students. This research was conducted using a standard procedure of instrument development, from the development of conceptual definitions, development of operational definitions, determination of constructs, dimensions, and indicators, to the preparation of blue prints, item preparation, expert validation, and testing. Data results from trials is analyzed using factor analysis and analysis of structural equation modeling (SEM). The data-analysis shows that there are 9 factors HOTS that construct the instrument with good validity and reliability. This instrument classifies high school students into five categories of HOTS ability. HOTS grouping results can be used by various interested institutions to evaluate the instruction of mathematics. These evaluations are used to determine the success of student learning and the success of teachers' teaching.