STEM fields do vary in job prospects.
MIT has a career survey of earned PhD graduates. The 2014 report is at https://gecd.mit.edu/sites/default/files/about/files/2014-edd-survey.pdf . Pay levels:
Major Post-doc Other
Pay Number Pay Number
Math 62950 10 215000 2
CS 76429 7 137000 5
EE 50754 14 132569 27
Physics 60026 19 131667 3
Chemistry 53941 8 103200 5
Biology 42600 12 97750 4
Civil Eng 46500 4 96024 5
Chemical Eng 43000 2 93375 12
Bioengineering 41650 4 87500 2
Materials Eng 48179 7 86000 5