This is a question that I think many others will benefit from, so I thank you for asking it.
From a strictly financial perspective, you probably would not realize a return on your educational investment in regard to increased salary. At public universities, the typical salary differential between bachelor’s and master’s degreed teachers is between 300 to 400 yuan, tops.
I should think that with an M.A. degree in linguistics or TESOL you would be very competitive for management positions at large private English language school chains—assuming you wanted to go that route (these companies work their DOSes* to death) but I couldn’t tell you off-hand what the salary differential would be. Certainly in terms of gross income, the difference would be much greater than the additional 200 or 300 yuan you would be paid at a public university but, of course, you would also be working much harder and longer for that money. If you do the math, the hourly rate for teaching 16 periods per week over a 34-week academic year at 5,000 yuan per month is considerably higher than earning 8,000 per month for a 18-hour week over 47 to 48 weeks—assuming, of course, the university pays their foreign teachers over the winter and summer vacations. Most still do.
I personally feel that education is never a waste of time or money but from a strictly financial perspective, the real pecuniary value in earning a master’s degree in TESOL or linguistics wouldn’t be fully realized unless you were willing to leave China—and it is in that limited context that I have recommended doing so to current foreign teachers, i.e. , as a way of preparing oneself for teaching ESL in a country other than China.
The only other caveat worth mentioning here is that at least one country, namely the United Arab Emirates, may discriminate against degrees that have been earned online. I read this on a popular EFL teachers’ forum and I have no idea if it’s accurate or not—but it might very well be. Of course, you have no intentions of moving to the UAE or anywhere else outside of China and I am guessing that this bias would not exist, certainly not to the same degree, here in the Middle Kingdom.
I wish I had better news for you. While a master’s degree in TESOL would certainly help you in terms of personal growth and self-fulfillment, it is unlikely you would recoup your financial investment in mainland China unless you were willing to work yourself to death.
Do you live close enough to Hong Kong to commute? If so, that would change matters considerably. The salaries there for an EFL teacher with a master’s degree in TESOL or linguistics would be several times what you can earn in mainland China.
*Director of Studies