The study aims to describe the development steps of the Higher-order Thinking Skill (HOTS) for the subject of trigonometric and their validation processes. Trigonometric is a subject that is considered difficult for learners due to the use of the mathematical concepts that are not real (abstract). While, the 2013 curriculum demands students to have critical, collaborative, communication, creativity, and innovation ability following 21stcentury necessities. In developing the HOTS problem, one should consider the curriculum, select the latest contextual stimulus, then validate and test it. The method used in this research is a qualitative method with a formative evaluation followed with a self-evaluation phase (Tessmer, 1993; Zulkardi, 2006). The results of this study are ten item problems of HOTS based on the C-4 framework (analyze), C-5 (evaluate), and C-6 (create). After being developed, the problem is tested on research subjects to check its validity, practicality, and potential.