In the technological disruption era, education goals have evolved to emphasize students to possess 21st-Century Skills. Learning model capable of accommodating these skills is a model that has a balance between a scientific approach and the use of technology. This research aims to develop a valid, practical, and effective Online-based Inquiry learning model to improve the 21st-Century Skills of physics students in senior high school. This research was research and development (R&D). The stages of model development consisted of preliminary research, prototyping phases, and assessment phases. The model was validated by five experts. Sixty tenth-grade students participated in the field test. The results showed that the validity of the model is on very high category. The practicality of the model is on very practical category. The average level of the students' 21st-Century Skills is 84.72, while the average N-Gain scores is 0.63. Based on these results, the model fulfills the valid, practical, and effective category for improving students' 21st-Century Skills and is expected to be an alternative reference to enhance the quality of physics learning and other fields of science.