Abstract: The aim of research is to describe the effectiveness of the inquiry learning model to improve the student’s high order thinking skills that have an impact on the completeness of the student learning outcomes at MAN 2 Gresik on the factors affecting the rate of reaction topic. This study used the One Group Pretest- Posttest Design. The data obtained from this research were as follows: (1) The implementation of the stages of the inquiry learning model showed that the percentage of implementation from the first to fourth meetings are 92.74%; 93.99%; 96.61%; and 97.13% with very good predicate. (2) The HOTS ability of students had increased. This could be seen from the pretest and posttest values processed with N-gain, getting a percentage of 96% in the high category and 4% in the medium category.