This is a very difficult question to answer. The simple answer is that an internship may make you more marketable to potential employers following graduation, so you may be able to get a higher-paying job. But it's unlikely that a company will offer you more money for the open position for which you're interviewing simply based on your internship. Of course, many companies list a potential salary range when listing available positions, and having that extra experience on your resume may give you a little more bargaining power than students who do not take the initiative to get this added experience. Yeah, it's not an easy question to answer.
If one thing is for certain, it's that an internship rarely hurts your chances of landing a job. A bad recommendation from a supervisor in a summer program or part-time program will not bode well if you try to use the experience in your favor. Working for a company that turns out to be a scam may not help you either. But good, solid experience from a legitimate company that earns you a positive recommendation letter will almost always help your chances of landing a job after graduation.
Make no mistake, though. An internship will not guarantee you a job by any means. It can only help you, as long as you take advantage of the opportunity. But you're not guaranteed an advantage over a student who did not participate in an internship merely because you did. It's essential to take the most from the experience as you can. That means working hard and soaking up knowledge as much as possible. Volunteer yourself to help people in the company or in your department in whatever task they may need assistance. Develop your skills and learn new ones. The experience can help your resume look great, but if you cannot transfer that into your interview you may not go very far.
So, again, while an internship may not guarantee that you'll make more money after graduation, it may help you land a job if you take the most out of it. Whether that job pays well is another story. Higher-paying jobs usually see competition from applicants with stronger resumes. Whether you belong in that class is up to you and the choices that you make throughout college. Then it's up to how fulfilling that experience on your resume was, and how it carries over into the real world.