The senior position is usually given to TL's who are seen as ETL potential but either do not have their degree or need some management experience. That said, they usually have all intentions of making you an ETL when they feel the time is right. You will basically have to go through an interview process similar to your TL interviews, however, they take place with your DTL and usually a call with your GTL. From there, they wait until a position opens and sign you off. They usually won't take you before or during 4th quarter to avoid being down an LOD during heavily shopped weeks.
So, the process is a bit different in that you have a much better shot than external applicants. Business college is the same, though.