Cisco Systems is among companies that say they are taking steps to improve diversity by forming diversity councils and employee resource groups and by tapping organizations such as the National Society of Black Engineers for job candidates. Cisco declined to released its most recent race data in detail, but said the number of black and Hispanic workers had "remained stable"

"Cisco believes an inclusive culture promotes creativity, innovation and drives collaboration," said Ken Lotich, a company spokesman.

The reasons Silicon Valley lags the nation in hiring — and perhaps in retention — of African-Americans and Latinos are varied and complex, researchers and observers say.

A company's commitment to diversity can waver, particularly in tough economic times, said Palo Alto venture capitalist Alberto Yépez, a former executive at Apple and Oracle. While Hewlett-Packard, for one, is consistent in its efforts, "I think companies that do not necessarily fare as well have issues, and it's the consistency that drives" successful diversity efforts.

Other reasons, experts say, include a history of valley companies hiring well-trained tech workers from the Pacific Rim, a weak pipeline of homegrown candidates, and a hypercompetitive business environment that leaves little time to develop workers.

"This is like 'top gun' school for techies. Basically, that's one difference between Silicon Valley and the other tech centers," said Vivek Wadhwa, a researcher at the University of California-Berkeley, Duke and Harvard who has studied the work-force dynamics of tech centers around the U.S. The intense premium on education "inherently gives Asians an advantage, because they tend to be stronger in math and science."

But social research has shown that innovation can flower from differences.

"If everybody around the table is the same, the same ideas will tend to come up. If you have a diversity of race, gender, age, educational and different life experiences, people will attack a problem from different perspectives, and that will lead to innovation," said Caroline Simard, research director for the Anita Borg Institute for Women and Technology. "In an industry that thrives on innovation, like high tech, it's especially important."

First-person account

Many minority tech workers are keenly aware of the numbers, because they live them every workday.

"I was the only African-American in every IT job I've ever had, " said Derek Anderson, a 24-year valley veteran who has worked at Adobe Systems, Cisco and other companies.

Like Anderson, San Jose State University computer science student Vicente De La Cruz describes a feeling of isolation — of being "the only one."

"I'm typically the only Latino, the only Mexican-American, in my class," said De La Cruz, a 34-year-old with a quiet demeanor. During a recent internship at the software company SAP in Palo Alto, he saw "maybe five other Latinos on the SAP campus. I've learned to adjust to it. You have to get used to it; it's a major motivation of mine to keep working in this field."

The Mercury News originally sought federal employment data for the valley's 15 largest companies through the Freedom of Information Act in early 2008. Following an appeals process that stretched over nearly two years, five of those companies — Google, Apple, Yahoo, Oracle and Applied Materials — convinced federal officials to block public disclosure. Data from 2005 was the most current available when the Mercury News made the request.

Between 1999 and 2005, Hispanics were a declining share of the work force in a majority of the 10 large Silicon Valley companies analyzed by the Mercury News — slipping to 5.2 percent of all workers at the 10 companies in 2005, from 6.8 percent in 1999. The black share of the work force at the 10 companies dropped to 2.1 percent, from 2.9 percent.

Even an organization as elite as Stanford's computer science department felt the need to revamp its curriculum this year, amid concerns that declining overall enrollment was causing the number of women, blacks and Latinos to dwindle even more.

As computer science enrollment dropped, "the percentage of women declined more than the overall percentage," said Mehran Sahami, a professor who led the curriculum reform. For the few women and minorities left, "suddenly it feels much more isolated" — yet another deterrent.

Women's prospects

Despite a few high-profile figures like Yahoo CEO Carol Bartz and Google search chief Marissa Mayer, labor department and other data suggest women are climbing the corporate ladder in Silicon Valley at a slower rate than men.

Over a recent lunch at the Women's Community Center at Stanford, gender researchers Simard and Andrea Henderson were recounting some gloomy statistics for a room of female computer science students.

In Silicon Valley companies, men and women in technical careers are equally likely to hold mid-level jobs, but men are 2.7 times more likely than women to be promoted to a high-ranking tech jobs such as vice president of engineering, or senior engineering manager, Simard and Henderson found in a 2009 study.

The researchers found a series of clues from the water cooler to the living room. Men are more likely to develop informal professional networks, like taking coffee breaks with colleagues — networks that often lead to career opportunities.

The valley's married male tech employees are more likely to follow the traditional model of having a man working full time, with a woman who stays home with the kids, than are male professionals nationally, perhaps because of the high salaries paid in tech. By contrast, tech women are overwhelmingly in dual-career couples, and many face an either-or choice — parenthood or career advancement.

"We expected a difference," Simard told the glum-looking students at Stanford, "but this is kind of like the 1950s."

Still work ahead

Simard and other researchers are convinced that valley companies do value diversity.

Take eBay, for example. While the San Jose company declined to make its executives available for an interview, or to share its most up-to-date employment information, eBay said it believes workplace diversity is crucial.

But the numbers don't reflect that.

As eBay's local work force swelled to accommodate the online retailer's growth between 2000 and 2005, eBay added 366 managers to its Silicon Valley offices. That net increase included just five additional black managers and no Hispanics.

At a time when eBay was headed by one of the few high-profile female CEOs in Silicon Valley, Meg Whitman, the share of the company's managers and top officials who were female declined to 30 percent in 2005, from 36 percent five years earlier, according to federal employment data.

"No global company today can stay competitive without persistently recruiting, retaining and developing a diverse work force "... eBay believes workforce diversity is critical to achieving our growth objectives and serving our millions of customers globally," the company said in a statement.

Some critics blame the government for allowing powerful Silicon Valley companies to rely so heavily on foreign-born workers on H-1B visas, which they contend has boosted the numbers of Asians in the tech workforce at the expense of other groups.

"The reason Silicon Valley is different is that those standards have traditionally been enforced in other industries," said John Templeton, whose "Silicon Ceiling" report details the lack of blacks and Latinos in Silicon Valley. "If you go to a bank IT department, or a cable television IT department, it reflects the community around it. But somewhere, government dropped the ball."

Others point to the public education system, noting that recent achievement test scores for black and Latino students have been even lower in Santa Clara and San Mateo counties than for the state overall.

"It certainly is a self-reinforcing cycle," said AnnaLee Saxenian, dean of the school of information at UC-Berkeley.

Aristotle Saunders, a 32-year-old Marvell engineer, volunteers with school kids in Oakland, dissecting iPods to interest them in a tech career. He thinks the lack of visible middle-class minority neighborhoods in Silicon Valley makes it even tougher to recruit minorities to tech jobs here.

"I sort of have that chameleon feel where I can fit in anywhere, but I can see where people raised in a black neighborhood would feel really uncomfortable," said Saunders, whose parents are African-American and Filipino and who grew up in a predominantly white neighborhood in Southern California. "Even though Silicon Valley is based on a principle of meritocracy, where they value people based on their skills rather than their class or ethnic background, I think it's still a challenge."