Starting out, the initial salary of a PhD in physics is significantly higher than of an MS in physics. And, if you graph the salary of the PhD and MS, you can see that they both increase roughly linearly over your career. However, surprisingly, the MS salary has a higher slope, so they both intersect roughly a decade out of school. After that, the PhD salary just can't keep up.

My thinking is that the MS earners go into management, which may not be worth the extra money. Depends on your personality.

These numbers are just statistics. There are people with PhDs who have amazing salaries, and those with MS who make little. Your mileage may vary.

Sometimes having a PhD helps during technical discussions, when it can be used as ammunition to back up your claims. However, these days management in most companies has decided that their MBA trumps a PhD from a top technical school. Another great situation for a PhD is when you need to represent your company to the outside world in some hot technical field - that piece of paper definitely makes people take you more seriously.

One nice trick is to get an MS in a top technical school. In the very rare situation when a technical discussion turns into "what degree did you get?", the answer "an MS from XYZ" usually terminates all doubts of your ability.

Me? Physics MS from a school that has 50 times more Nobel prize winners than my coworkers' school. There have been two situations where the lack of PhD had an effect: (1) almost was not hired into a group of PhDs doing exciting work but they assumed I had one and hired me, and (2) during a period of college-level teaching I was told I had no chance at tenure.
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