NEW YORK (CNN/Money) - Sun Microsystems Inc. said Wednesday its president and chief operating officer, Edward Zander, has decided to retire from his full-time duties with the network hardware company.

Zander, 55, will hand over his duties to Chairman and CEO Scott McNealy on July 1, the end of the company's fiscal year, but will stay on to assist with the transition and begin a teaching and mentoring role for the rest of 2002.

Shares of Sun Microsystems (SUNW: down $0.85 to $7.33, Research, Estimates) fell almost 10 percent in early trading Wednesday.

Zander is the third top-level Sun Microsystems executive to step down in recent weeks. Chief financial officer Michael Lehman announced his retirement last Thursday, and John Shoemaker, executive vice president of the company's core computing systems business, announced last month he will step down effective July 1.

"I am proud of all that we have achieved at Sun," Zander said in a statement. "This is a decision I have considered carefully over the past year. As we are marching down the path back to profitability, and have, for the most part completed our massive product and customer engagement transitions, I believe I have accomplished what I set out to do."

Sun has no plans to name a successor to Zander, as McNealy will take over the role of president in addition to his current duties, and oversee Zander's staff.

"Over the last 15 years, Ed has worked tirelessly to lead Sun through several transformations and to the forefront of the computer industry," McNealy said.

As president and chief operating officer, Zander runs the company's day-to-day business operations and has been responsible for finding ways to implement Sun's goal to be one of the largest suppliers of network products, technologies and services.

Prior to being named chief operating officer, Zander was president of Sun's computer systems business and held other management positions at the company. Before joining Sun he was a manager at Apollo, Data General and Raytheon.