One of the longest-tenured CEOs in Silicon Valley is passing the torch.

On Monday, Cisco Systems announced that John Chambers, the company's CEO since 1995, will be succeeded this July by longtime company executive Chuck Robbins, who is currently the networking giant's senior vice president of worldwide operations. Chambers will remain at Cisco as executive chairman and continue as chairman of the board.

The move marks a significant changing of the guard from one of Silicon Valley's legendary leaders to the next generation. Chambers is one of only about two dozen CEOs of S&P 500 companies who have been at the helm for at least two decades, according to S&P Capital IQ. And he has been running the largest tech company by far among those long-tenured chief executives, after Larry Ellison announced last year that he was stepping down from Oracle.

Chambers's 20-year tenure means his succession plan at the networking giant has been speculated about for years. Still, the choice of Robbins was said to be something of a surprise. Although Robbins was among those mentioned in 2o12 as being under consideration as successors, company insiders reportedly expected the position to go to either Rob Lloyd, who is Cisco's president of development and sales, or Padmasree Warrior, its chief technology and strategy officer.

During his reign at the top of the company, Chambers oversaw the company's growth from $1.2 billion in annual revenue to $47 billion. He managed the company through a near-death experience following the bursting of the dot-com bubble in the early 2000s, and has recently led the company through a restructuring that included a series of job cuts. Cisco's most recent quarter showed a rebound in growth.

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