California and Massachusetts have become the leading US states investing in clean tech. As a recent article in the CSMoniter points out,
Global investment in clean-tech research and enterprises approached $100 billion in 2007, and much of that money was invested in the United States. Of about $3 billion in “green” venture capital worldwide, half went to enterprises in California, and Massachusetts got about 10 percent.
The article goes on to point out that half of all US states have now launched initiatives to aggressively grow clean tech industries. In terms of jobs alone, clean tech now employs more than 14,500 people in Massachusetts, growing at a rate of 20% per year.
Among the reasons listed for how some states have been able to successfully grow such robust clean tech industry: access to graduates from good universities, increased government support, access to local resources and raw materials.