Amelio, who was ousted from his job at Apple, was also CEO of National Semiconductor. Some industry analysts and former employees blamed Amelio for Apple's decline.
A spokesman for Sienna Ventures declined to comment. Amelio couldn't immediately be reached for comment.
Currently the managing director of Beneventure Capital, Amelio will join Sausalito, Calif.-based Sienna this month, according to sources.
Sienna primarily invests in wireless communications, networking, Internet infrastructure and software companies seeking early rounds of financing. The firm, formed in 1990, has invested in such companies as Epana Networks, a communications company that is developing ways to reduce network congestion, and M7 Networks, a service provider for mobile Internet hosting.
In February the firm closed its Sienna LP III fund, which raised $75 million from such investors as the California Institute of Technology and First Union Bank.
Also in February, Advanced Communications Technologies--an Australia-based software company--said it would acquire Beneventure Capital. ACT USA, based in Los Angeles, was interested in the complementary nature of Beneventure's portfolio companies and its wireless technology.
Amelio "chose Sienna partly because he will be able to devote more attention to a smaller number of portfolio companies," the source said.
Partners at Sienna typically sit on half a dozen boards of its portfolio companies, the source said. Sienna has a history of taking an active role in working with a company's management, and Amelio has a background in managing large companies.