LOS ANGELES, Sept. 2 (Xinhua) -- Silicon Valley, burdened by high housing costs, congestion and unemployment rate, lags behind other 11 technology hubs in the U.S., according to a survey.

Silicon Valley ranks last in an annual ranking of 12 U.S. technology hubs because of the region's notoriously high housing costs, traffic congestion, unemployment rate and other quality-of-life problems.

This was the second straight year that San Jose, California-based Silicon Valley ranks last of 12 U.S. technology hubs, said the survey by the Silicon Valley Leadership Group (SVLG).

The survey, made public on Saturday, ranked North Carolina's Raleigh-Durham area as the nation's top-ranked tech hub for its relatively affordable housing and a thriving job market. The region also wins points for local children's performance on eighth-grade math tests as well as low sales taxes and utility bills.

Seattle, home to thousands of well-paid technology professionals who work at Microsoft Corp. in suburban Redmond, Washington, comes second, to be followed by the greater Denver area, which despite increasing traffic jams and soaring housing prices is home to many start-ups in the emerging alternative-energy niche.

Expensive cities such as New York or those with struggling urban cores such as Philadelphia and Chicago, which were not included in last year's list, all finished higher than Silicon Valley this year.

"These results were a reality check on the challenges we all know we face here in the valley," said Carl Guardino, president and chief executive of the SVLG, which represents more than 200 private-sector employers. "There are seemingly intractable challenges we know won't change over a week or a year."

The valley, stretching from San Jose north to San Francisco and Berkeley as well as suburbs such as Cupertino and Palo Alto, fared particularly poorly because of its expensive homes.

Only 14.9 percent of local homes are within the price range of individuals earning the median income, according to a home builders survey included in the group's study. By contrast, 65.8 percent of homes in North Carolina's Raleigh-Durham tech hub are within the reach of those earning the median income.

Despite its poor showing, Silicon Valley has plentiful capital, attracting nearly 8 billion dollars annually in venture funding, four times as much as its closest domestic rivals. That includes 1.6 billion dollars for "clean technology" and alternative-energy companies, according to the survey.

Silicon Valley also is one of the world's few tech hubs that dominate both the technology and life-sciences industries, put tingit above international centers such as Basel, Switzerland; Bangalore, India; Prague, Czech Republic; Dublin, Ireland; Berlin; Tokyo and Shanghai.

The effect of weather, cultural attractions or other intangibles that draw many people to California were not considered in the survey. Enditem