Joy Ying Zhang, the son of a primary-school teacher and a college professor, left China's Hunan Province in 1999 for Detroit's Wayne State University, where he arrived with two suitcases and $2,000 in cash.
He later transferred to Carnegie Mellon University, which awarded him a PhD in computer science in 2008.

Four or five of his friends have returned to China, he said, and he has discussed doing so. But Zhang, now a research assistant professor at Carnegie Mellon's Silicon Valley campus, has decided to stay. "I have spent 10 years here already," he said. "It took me some time to get used to American life. Now, it'd be hard to get used to China. It's called `reverse culture shock.' " Zhang, 35, has a brother who works for a pharmaceutical company in the US and a sister who is a physician in China and close to their parents.

In recruiting for Carnegie Mellon, he finds young Chinese less eager to come to the US than those of his generation. "Life in China is getting better. There are research alternatives in China--like Microsoft China," he said. "They can get good mentoring and advice there, instead of coming to the US."

In 2007, foreign citizens accounted for 16,022 of the PhDs awarded in science and engineering in the US, or 46% of the total, according to the Oak Ridge data. In contrast, the class of 1997 had 12,966 foreigners, or 30% of the total.

Graduates of PhD programmes in the physical sciences and computer science are more likely to remain in the US than those in other fields, Finn said. Those programmes are popular with Chinese and Indian students, who are more likely to remain in the US after completing studies than those from Taiwan, South Korea and Western Europe. Among 2002 graduates, 92% of the Chinese and 81% of the Indians were in the US after five years; in contrast, 41% of South Koreans and 52% of Germans were.

Aranyak Mehta, 31, came from India nearly a decade ago to study the science of algorithms at Georgia Institute of Technology and earned a PhD in 2005. Today, he is a research scientist at Google--and planning, for now, to remain in the US. "There's always a tradeoff--family, culture, and all that," he said. "One of the most important things with an academic background is the work that you do, and is it exciting?
I'm not saying there is no exciting work in India. Many people have gone back and started companies."

Using the LinkedIn online network, Wadhwa identified 1,203 skilled Indians and Chinese who had returned home.
Three-quarters said visa issues weren't a factor. Rather, career opportunities, quality-of-life concerns and family ties were major factors. Some 70% of the Chinese and 61% of the Indians said opportunities for professional advancement were better at home.