The Higher-Order Thinking Skill Test Instrument on Quadratic Equations (HOTS-QE) was developed to measure the level of HOTS on the topic of quadratic equations among secondary school students. The HOTS-QE instrument consists of 17 structured subjective items divided into two smaller questions according to the three levels of HOTS, namely applying, analysing, and evaluating. This study proposes a design and development research (DDR) approach via a development research that was done through an organised and systematic process. The DDR-oriented development process comprised seven stages namely source analysis, theory, development, content validity, validation of the HOTS domain accuracy, language validity, and pilot study. The development of the HOTS-QE instrument comprised seven stages, namely source analysis, theory, development, content validity, validation of the HOTS domain accuracy, language validity, and pilot study. The content validity of the instrument was evaluated by five mathematics education experts. The results showed that the item content validity index (I-CVI) value of each item was above 0.70 while the content validation per scale (S-CVI) value was 0.98. Results from the interrater evaluation also showed that the HOTS level accuracy of the instrument items had achieved the Cohen's Kappa coefficient value of 0.63. In addition, findings from the pilot study also showed that the Cronbach's alpha coefficient value was 0.79, the discrimination index value of each item was between 31.11% to 66.67%, and the difficulty index values were between 40.74% to 70.00%. These results suggest that the HOTS-QE instrument has an acceptable level of validity. The development of this instrument provides a more varied learning assessment that can foster students' interests in learning, help them to improve HOTS, and provide opportunities for students to directly apply the knowledge of quadratic equations learned at school in their daily life.