The Master Scuba Diver rating is the highest recreational diver rating in the PADI program, and denotes superior achievement and proficiency.
Achieving the Master Scuba Diver rating requires that an individual be certified as:
Submit an application for the rating, in addition to evidence of completion of all required certifications, and a photo to the appropriate PADI Office for review and approval. The application may be submitted by any Teaching status PADI Instructor. Although a Master Scuba Diver Trainer rating exists, this certification is not a requirement for the instructor to submit a Master Scuba Diver Application.
You can download an application form (PDF) here.