It depends on the hiring rate at your university. Look at this year's graduates and see what percentage already have a job lined up. If it's 100%, then the internship may not be worth the bother. If you have friends who are graduating this year - [and if they're in you major at the same university and you're a sophomore and junior, then you SHOULD have made friends with a couple of the upper classmen in your major (that whole networking thing that often goes unexplained to people)] - then find out if those who did internships are getting better paying jobs than the others. If that's the case, it becomes a math problem. I know that in my son's major, 100% of this year's graduates in his major had job offers prior to graduation. He got a much sweeter deal than many of the other students, probably because of his internship experience. In his case, it didn't set him back a semester. However, in my opinion, even if it would have, it was worth the difference in job satisfaction that working at a better company (plus a little bit more pay) gained him.
Think of it this way:
semester semester semester semester semester work semester semester work
or
semester semester semester semester semester semester semester work work
Notice that those lines are the same length, and contain roughly the same amount of time being paid to work. The internship will likely pay less, but could make up for it by getting a better job paying more - after half a year of work, you might break even on the pay, then be ahead after that. The second line is based on the assumption that you have a job lined up before you graduate - you might not find a job as quickly if they all say "experience desired."
However, if 70% of the graduating students have jobs lined up, again, take a look at the qualifications of those who were hired vs. those who weren't hired. If it seems that those who had done internships were first to get hired, then the decision is a no-brainer. Take a semester off and get paid for working, and get job experience? Or spend an equivalent amount of time after graduation looking for a job and NOT getting paid while you do it.