This study aims to develop a mathematics learning application, namely Android-based mobile learning to increase students' High Order Thinking Skills (HOTs). The result of mathematics learning media is a valid and practical mobile learning application product. "Mastering Math" is the name of a mathematics e-learning application designed as a mobile or smartphone application, with specifications for the OS Android. The procedure for the development of virtual mathematical media used the development of the 4D model of Thiagarajan: (1) define; (2) design; (3) develop, and (4) disseminate. The trials conducted included five expert judgments and a small group. The research instruments used were a validation sheet, a practical assessment sheet by the teacher, a practical assessment sheet by students, and a media effectiveness test instrument. Data analysis was performed using Cochran's Q test for similarity of expert validation and qualitative analysis. The teaching materials used are junior high school teaching materials with validity and practicality in the good category to increase students' HOTs. This research implies that the learning of mathematics is more effective and efficient, students' divergent thinking develops, and their learning motivation for mathematics increases.