Switch fields from Physics to Electrical Engineering in US: MSc vs BSc? My brother wants to switch to Electrical Engineering and possibly do a Master's degree (with thesis). He also has a BSc and MSc degree in physics but not much formal training in EE (except some basic electronics, solid-state physics and advanced electromagnetism courses). 

Since the most important factor in grad school applications is research, he has tried to contact professors and labs so many times for even non-paid internships, with no results. The other option is to apply to BSc degree or just about any MSc degrees in order to take the prerequisite courses. 

How should he proceed? What are some advantages or disadvantages of getting a BSc in EE (using some credits from the previous degree) vs doing a Master's program in EE with thesis that accept him and take the prerequisites courses?
It depends on his goals.  Since he wants to do research, it doesn't matter that much whether he has a BSc or a master's as long as he can convince the department he applies to for his PhD that he has the necessary knowledge.  A master's might be slightly better since he will naturally get more research experience, but it is possible to get research experience as an undergrad by volunteering in your professors' labs.  The disadvantage of going straight to a master's is that he won't have the same background as the other students.  This means that either (a) the department will ask him to take prerequisite courses, at which point the master's program will take almost as long to finish as the BSc, or (b) he will be expected to catch up with the other students on his own time, which will be a lot of work.

If he thinks he might want to work in industry at some point, I would recommend doing the BSc.  Engineering is a professional designation in the US, so without the BSc, he can't call himself an engineer.  This doesn't mean he can't get hired, but it means he will get hired under some other job title ("technician", say) and may get paid less than he would if he were hired as an engineer.  Considering that this would affect his whole career, I would recommend investing the extra time up front, especially if he can shorten the BSc by reusing some credits from the physics degree.