Goeckeler served as executive vice president of Cisco’s networking and security businesses.
He will join Western Digital on March 9. He also will serve on the board of the maker of disk drives and memory chips.
"With experience as a software engineer as well as running large semiconductor development projects, his breadth of technology expertise, business acumen and history of building and operating world-class organizations make him the right person to lead Western Digital in a world increasingly driven by applications and data," Chairman Matthew Massengill said in a statement.
Milligan has served as CEO of Western Digital since 2013. He announced in October plans to retire. He will remain with Western Digital as an adviser until September.
Shares of Western Digital were inactive in premarket trading. The stock closed Thursday at $57.71, down 2.42%. The stock has fallen 9% year to date.
Clemmer had served as CEO of NXP since 2009 and the company said he will remain a strategic adviser to the company.
Sievers’ appointment as CEO will be proposed at NXP’s annual shareholder meeting on May 27.