Indian immigrants in the US are making a strong mark for themselves with an ever increasing number turning into inventors in the country, a recent study says.

According to a report prepared by a team of researchers from Harvard, Duke and New York Universities, the number of Indian nationals contributing to US international patent applications touched 5.5 per cent in 2006.

This is a sharp rise compared to just 1.6 per cent in 1998. "During this period, there was a large influx of highly educated Indians into US and they contributed immensely to the intellectual capital of American corporations and universities," Vivek Wadhwa, a fellow at the Harvard Law School and executive-in-residence at Duke University, one of the authors of the report told PTI.

Analysing the Patent Cooperation Treaty applications from the US at the World Intellectual Property Organisation, the researchers found contribution of inventors with Indian-heritage names increased to 13.7 per cent from 9.5 per cent during 1998-2006 period.

Besides, Indian and Chinese inventors file most patents in the fields of sanitation, medical preparations, pharmaceuticals, semiconductors and electronics.

Geographically, most of the Indian inventors chose to reside in places like California, New Jersey and Texas.

"Indian-born entrepreneurs in the US founded more engineering and technology firms (from 1995-2005) than the next immigrant groups -- from UK, China, Taiwan and Japan, combined." the report revels.

The researchers also examined information published by the US Homeland Security Department, Labor Department and State Department Immigration Survey to understand the foreign-national data.

Titled 'Intellectual Property, the Immigration Backlog and a Reverse Brain-Drain, America's New Immigrant Entrepreneurs', the report also throws light on the contributions from foreign nationals and foreign residents in filing international patent applications from US.

Meanwhile, Chinese inventors saw their contributions rising to 6.2 per cent in 2006 from 1.8 per cent in 1998.

"Chinese people were number one in filing global patents but then Chinese population is also greater than Indian," said Wadhwa.

Foreign-national inventors are individuals with foreign citizenships working in the US while foreign-resident inventors have foreign citizenship and are not based in US.

The data for 2006 shows foreign nationals residing in US were inventors or co-inventors of one in four US PCT applications, a more than three-fold increase compared to 1998. The percentage of foreign nationals contributing to US international patent applications increased to 25.6 per cent in 2006 from just 7.6 per cent in 1998.

Delving deeper into the 2006 statistics, more than half of the international patents filed by large multinational companies were contributed by foreign nationals and foreign residents. Qualcomm Inc saw a contribution of 72 per cent followed by Merck (65 per cent) and General Electric Company (64 per cent), Siemens (63 per cent) and Cisco (60 per cent).

Interestingly, Microsoft (3 per cent) and General Motors 6 per cent) had the least contributions from foreign nationals, the report said.