Karen Mills, the head of the Small Business Administration, has told President Obama that she will be leaving her position.

Who will replace Mills remains unknown. The White House is making no personnel announcements today, according to an email from White House spokesperson Inouye Shin. Mills said in a letter to staff that she will stay on until the White House has named a replacement.

Mills served as the 23rd head of the government agency that is charged with representing small business interests in Washington. She was sworn into her position in April 2009.

Related: Google Hangout with SBA Chief Karen Mills

In a nod to the important role small business plays in the economic recovery, Obama elevated the Administrator to a Cabinet-level position in January of 2012. The announcement was made as part of a larger proposal from the White House to merge the agency with five others in a bid to make government more efficient. The president would need Congress to sign off on his broader plan to streamline agencies, and since the announcement in January 2012, there has been no further action on the proposal.

Mills came into the SBA as the recession had choked off pipelines of credit to the nation's small businesses. During her time at the SBA, she worked to implement various stimulus measures to improve access to capital. In its 2011 fiscal year, which ends Sept. 30, the SBA supported more than $30 billion in lending to more than 60,000 small businesses throughout the U.S.

Related: Small Business and the President's Cabinet (Video)

In her four years heading the agency, the SBA supported more than $106 billion in lending to over than 193,000 small businesses and entrepreneurs, Mills noted in her letter to staffers.

President Obama thanked Mills for her work in a written statement, noting her key role in passing the Small Business Jobs Act and her efforts to reduce paperwork and bureaucracy in the agency.

Before coming to the SBA, Mills was president of the private-equity firm MMP Group, which invested in businesses in the consumer products, food, textiles and industrial components industries. Also, in 2007, the governor of Maine appointed Mills to be the chair of Maine's Council on Competitiveness and the Economy where she worked to revive Maine's boatbuilding industry by helping the craftsmen cluster together. She was always a proponent and fan of clustering as a way to develop region economies.

Related: A Cluster of Clusters: Where the SBA Is Investing in Regional Economies

Who would you like to see replace Mills as the next head of the SBA? Leave a note below and let us know.