College tuition is on the rise across the U.S., and University of California President Janet Napolitano says she knows why.

In a report last year, the College Board showed the price of a four-year degree rose faster than the rate of inflation, with private tuition climbing by 3.7 percent to an average of $31,231. At public universities, the picture was scarcely better: Costs jumped by 2.9 percent during the academic year to $9,139.

However, in an interview with CNBC's "On the Money," Napolitano says UC students should blame state budget cuts—and not the universities themselves—for higher tuition bills.

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"The chief cause of the cost to students going up is the fact that public investments in our universities have gone down. There are two major sources of revenue to operate quality institutions: state appropriations and tuition," Napolitano said.

"And when state budgets go down … unfortunately tuition has had to go up," she added. (Tweet this)

Napolitano says she hopes the money will be coming back to education—in her state, at least. "As state budgets are restored, as monies come back into the coffers, we're advocating it's time to reinvest in the University of California and the Cal State University system."