Shirley M. Tilghman, Princeton's first woman president, as well as one of two college chiefs on the board of Google (Nasdaq: GOOG), said she'll step down next June after serving 12 years in the post at one of the world's top universities. Tilghman, 66, said she'll take a year's leave and then return to teaching microbiology.

The retirement was not expected, a university representative said. In the past, Princeton has established search committees to recruit a new president. Tilghman herself was on the last one, set up in 2000 when economist Harold T. Shapiro announced he would retire. She succeeded him in June 2001.

Tilghman, 66, a native of Canada who was selected as Princeton's first female president since 1746, has served on the board of Google, of Mountain View, Calif., since 2005, a year after its initial public offering. Her resignation announcement made no mention of anything concerning Google, whose Chairman and former CEO Eric Schmidt is a Princeton alumnus who served as Princeton trustee during Tilghman's tenure. Schmidt and his wife, Wendy, also donated $25 million to Princeton in 2009.

Stanford University President John Hennessey is Google's lead independent director. The two university presidents have helped Google open doors to academic institutions and libraries where Google wants to scan books and documents to make them available online.

Tilghman is a molecular biologist who received undergraduate degrees from Queen's University in Ontario and a doctorate from Temple University. "These years have been joyous ones for me and the highlight of my professional career," she said in a note that cited many accomplishments expanding Princeton's science and liberal arts offerings.

Based in Princeton, N.J., the university currently enrolls about 7,600 students in undergraduate and graduate schools.

Shares of Google closed at a record high of $733.99, up $5.87, on Friday.