American students are increasingly questioning the value of college. According to a recent survey conducted by Gallup and Purdue University, nearly 40% of U.S. college graduates say their education wasn’t worth the cost. And they may very well be right.

On the other hand, there still exist colleges where the money you fork over for tuition and board might actually be worthy of the term “investment.” Each year, PayScale provides a ranking of the colleges with the best return on investment (ROI). The rankings are calculated based on the difference between the 20-year median pay of a graduate from the school and its total 4-year cost.

Here are the 20 schools with the best ROI according to the 2015 rankings:

1. Harvey Mudd College (CA)

2. California Institute of Technology

3. Stevens Institute of Technology (NJ)

4. Colorado School of Mines (In-state tuition)

5. Babson College (MA)

6. Stanford University

7. Massachusetts Institute of Technology

8. Georgia Institute of Technology (In-state tuition)

9. Princeton University

10. Colorado School of Mines (Out-of-state tuition)

11. Virginia Military Institute

12. Kettering University (MI)

13. Rose-Hulman Institute of Technology (IN)

14. Missouri University of Science and Technology

15. Brown University

16. Worcester Polytechnic Institute (MA)

17. Georgia Institute of Technology (Out-of-state tuition)

18. NYU Polytechnic School of Engineering

19. Rice University

20. University of California-Berkeley

So what are the characteristics of the schools with the best ROI?

Number one: reputation and selectivity. Many of these schools are consistently among the top colleges in the annual U.S. News and World Report rankings. They not only provide one with access to some of the best professors in the country, but also (and perhaps more importantly) they provide one with prestige and with connections to successful alumni and soon-to-be successful students.

Number two: they specialize in areas with high salaries. Among the majors with the highest starting salaries, engineering-related ones occupy the top 10 slots, followed by other STEM fields such as computer science, mathematics, and physics. Many of these schools in PayScale’s list are considered among the top schools for these majors.

If the college you’re planning on attending does not fit either one of these criteria – if it is not a top-tier school or does not have reputable departments in STEM majors – you may indeed want to reconsider if the tuition is worth it.