For the first time since going public in 1995, Brooks Automation Inc. added a woman to its board of directors this year.
The Chelmsford company, which makes robotics and vacuum components for the semiconductor industry, brought in Ellen Zane, the former president of Tufts Medical Center, to help with its expansion into the life-sciences sector.
"The questions that she asks are questions in some regards that we've never asked ourselves," said chief executive Stephen Schwartz.
Brooks is one of six major Massachusetts companies to add women to their previously all-male boards in 2012, contributing to a record high of 108 women board members at the state's 100 largest public companies, according to the annual census of female directors and executive officers by the Boston Club, a women's business group.
But women's advancement into the top echelons of the corporate world remains slow and uneven.
Women hold only about 13 percent of directors' seats at Massachusetts' biggest public companies, and one-third of these firms have no women on their boards.
In addition, while the number of female executives increased slightly from last year, it remains below the levels of 2005 to 2007. About half of the state's 100 largest public companies have no female executive officers, according to the survey.
"Achieving any level of gender diversity has been and continues to be a slow process," said JoAnn Cavallaro, president of the Boston Club. "We continue to keep our heads down."
Companies nonetheless are becoming more aware of the importance of diversifying their leadership teams, Cavallaro said, realizing that getting different opinions and employing people who represent diverse customer bases is a smart business move.
There is also more pressure on companies to diversify their top ranks from shareholders and state treasurers, including Steve Grossman of Massachusetts.
Grossman issued guidelines that consider the presence of women in executive suites and in the boardroom when investing state pension funds.
Groups such as the Boston Club and 2020 Women on Boards, a national campaign based in Jamaica Plain to increase the percentage of women on corporate boards to 20 percent by 2020, have also called attention to the issue.
That pressure is helping put a premium on female executives.
After Zane retired from Tufts Medical Center, she was approached by 10 companies about joining their boards, she said. She serves as a director for three companies.
"They are absolutely thirsty to have us come onboard," she said.
Still, fewer than 10 percent of the executive officers at the 100 companies surveyed are women, down from 11 percent in 2006. A quarter of the companies have no female executives or directors.
A number of large Massachusetts companies that had multiple women in their boardrooms and executive suites were acquired or went private in the past 10 years, the Boston Club survey notes, and were replaced on the list of top 100 companies by smaller companies in male-dominated industries such as technology and manufacturing.
"There's a tendency for small companies to lag with respect to the percentage of women on boards," said William Bacic, chairman of the Boston Club's corporate advisory board.
Nationally, women account for about 16 percent of the directors and 14 percent of executive officers at Fortune 500 companies. In Europe, some countries have put quotas in place, or are considering doing so, to increase the number of female board members.
This probably would not fly in the United States, said Elliot Schwartz at the Committee for Economic Development, a nonprofit public policy research organization in Washington. But as European companies start to recruit American women for their boards, it could pressure US companies to follow suit.
"If we're going to win global races for competition and so on, they need to provide more openings and opportunities for women," Schwartz said. "If they don't they're giving up a valuable resource."