Fiorina, one of the most powerful women in business, had been with the computer and printer maker since 1999. HP said a search for a new CEO was underway immediately.
"While I regret the board and I have differences about how to execute HP's strategy, I respect their decision," Fiorina said a statement. "HP is a great company and I wish all the people of HP much success in the future."
Robert Wayman (search), HP's chief financial officer, was named CEO on an interim basis and appointed to the board of directors of the computer and printer maker. Wayman rose through the ranks at HP after joining the company in 1969.
Patricia Dunn, vice chairman of Barclays Global Investors and a member of HP's board since 1998, was named non-executive chairman of the board.
The announcement came after recent reports suggested the HP board of directors had discussed shifting some day-to-day responsibilities from to other executives in an effort to improve the technology giant's performance.
Fiorina, one of a few women to lead a Fortune 500 company, pushed through HP's acquisition of Compaq Computer Corp. (search) in 2002 despite fierce resistance from shareholders and directors.
In recent months, she has been the target of intensifying criticism from technology analysts and the media for her ambitious diversification strategy — an attempt to change HP from a relatively marginal company that focused on printers and ink into a Silicon Valley consulting and computing powerhouse.
Despite her efforts, the company's printers and ink division has remained HP's profit center. HP has also faced more than two years of withering competition from Dell Inc., which revolutionized the sale of low-margin printers, and IBM Corp. (IBM), which is focusing on lucrative consulting contracts.
Appearing at the World Economic Forum last month, Fiorina tried to downplay a Jan. 24 report in The Wall Street Journal that said HP's board was considering shifting her day-to-day duties to other HP executives.
At the conference in Switzerland, she called the report "speculation" and said her relationship with the board remained excellent.
"Carly Fiorina came to HP to revitalize and reinvigorate the company," Dunn said in a statement Wednesday on behalf of the board. "She had a strategic vision and put in place a plan that has given HP the capabilities to compete and win. We thank Carly for her significant leadership over the past six years as we look forward to accelerating execution of the company's strategy."
Analysts Laud Departure
Analysts and investors said her departure would be good for the company.
SG Cowen analyst Richard Chu said Fiorina's ouster would help HP shares. "The fact that everything is back on the drawing board, with respect to (spinning off) the printer business, makes the stock more attractive," he said.
"This was a move that we had long hoped they would take. We thought the stock, just from the imaging business, is worth $24 a share, and you were being impaired as a shareholder because of the other businesses," he said.
"I would say there will be a boost to employee moral because internally people had become frustrated," said Shannon Cross, a Wall Street analyst with Cross Research who tracks the printing industry.
Bear Stearns cut its rating on HP shares to "underperform" from "peer perform," saying major operational challenges remain. Analyst Andy Neff said the share price, including the 10 percent rise in early trading, reflected most of the possible gain from a potential break-up of the company.
HP's stock has languished since the Compaq deal, Inconsistent quarterly results led to several sharp sell-offs in the shares in recent years.
HP shares climbed $1.26, or 6.3 percent, to $21.40 in midday trading on the New York Stock Exchange, still well shy of its 52-week high of $25. Its 52-week low was just above $16 in August.
Reuters and The Associated Press contributed to this report.