The 51-year-old Appleton, a three-decade industry veteran who performed stunts at airshows, died after the small plane he was piloting crashed at an airport in Boise, Idaho, where the chipmaker is headquartered.

His death stunned the tight-knit semiconductor industry. Appleton was a prominent figure in Boise, a city of 200,000 in the western United States, and a member of the Idaho Business Council.

President and Chief Operating Officer Mark Durcan, who was due to retire in August, will take up the CEO's responsibilities until the company's board can appoint a permanent successor. Directors will meet over the weekend, Micron said in a statement.

Shares in Micron, halted prior to the announcement, resumed trade after the regular market close and promptly slid 6 percent.

"Steve was a high-energy, never-give-up type of inspirational leader of the company. The entire industry will miss Steve's energy," said Stifel Nicolaus analyst Kevin Cassidy. "That said, Micron has a deep bench of managers that shared Steve's vision."

The accident happened while Appleton flew an experimental Lancair single-engine airplane, Boise Airport spokeswoman Patti Miller told Reuters. Lancair sells kits to build high-end planes.

After taking off and reaching an altitude of about 200 feet, Appleton radioed that he had a problem and needed to turn around, Boise police spokeswoman Lynn Hightower told reporters.

The aircraft rolled left, then plummeted to the ground, where it crashed, causing a large fire and leaving a twisted, black wreckage.

Appleton, a California native, joined Micron to work a night shift right after graduating from Boise State University in 1983. His subsequent meteoric ascent led to his becoming the youngest CEO on the Fortune 500 at the age of 34, in 1994.

He resigned in 1996, amid speculation about a boardroom power struggle, only to return nine days later after the board asked him to reconsider.

Appleton, a noted sports enthusiast who also scuba-dived, surfed and raced offroad cars and motorcycles, received the prestigious Robert Noyce award - the industry's highest honor - from the Semiconductor Industry Association in 2011.

The award, named after Intel Corp cofounder Robert Noyce, is conferred on those who have made major contributions to the chip industry.

Employees at Micron's sprawling headquarters and plant, where several flags flew at half mast, were visibly upset while others stuck to routine.

"I was in a meeting, which proceeded normally, but at the end when it broke up it was nothing but sad talk about Steve." said employee Mike Peterson. "I know he liked airplanes so if he was going to go I guess this was fitting."

Co-worker Melanie Wood said: "Someone told me over my cubicle and then I read the email and we all didn't believe it at first. He's so young, you don't expect something like this."

A BIG LOSS

"Steve was a visionary and a true leader in our industry. He will be deeply missed by the entire semiconductor community and our prayers and thoughts are with his family," Brian Toohey, President of the Semiconductor Industry Association, said in a statement.

Micron makes memory chips used in personal computers, smartphones and tablets and competes against Asian rivals Hynix Semiconductor Inc, Samsung Electronics Co Ltd and Toshiba Corp.

Memory chip makers are struggling as falling prices and huge investments to stay competitive saddle them with massive losses. Micron is the last remaining U.S. producer of memory chips.

Boise Mayor Dave Bieter said Appleton was sensitive to how job cuts by Micron in recent years affected the community.

"He called me and told me about the layoffs coming up and explained how the business-end of chip technology would develop and that Micron would come out strong on the other end. And it happened exactly the way he said it would," Bieter told reporters.

The company announced just last week that Durcan would retire in August, but Appleton's death raised questions about whether he might stay on.

Seen as Micron's even-keeled top technologist, Durcan has taken on a greater role running the chipmaker day-to-day in the past few years, while larger-than-life Appleton has focused more on strategy.

The loss of Micron's dealmaker could waylay a possible acquisition of troubled Japanese rival Elpida Memory. Saddled with millions of dollars in operating losses and major upcoming debt payments, Elpida may be in talks to be bought by Micron or reach some kind of partnership, media recently speculated.

RISKY LIFESTYLES

Appleton's death raises questions about whether some CEOs' daredevil lifestyles are too risky for shareholders.

British tycoon Richard Branson has tried to circle the world in hot air balloon and in 1985 had to be rescued after capsizing a sailboat. Oracle co-founder Larry Ellison races sailboats and also flies planes.

Micron's recent regulatory filings make no mention of a "key man" life insurance policy on Appleton, nor do they specifically mention directors' and officers' insurance that would cover him.

A senior executive at a national insurance brokerage said it is entirely possible to get directors' and officers' insurance on someone like a CEO who flies his own planes, but added that Appleton's death could still cause legal headaches for the board.

"D&O really is about, at its core, for a public company, whether or not the company is susceptible to litigation by shareholders," said the broker, speaking anonymously because of the sensitivity of the matter.

The broker said Micron's board would have an obligation to have a contingency plan in place, particularly given Appleton's risky lifestyle, and that the degree to which the company might face legal questions depends a great deal on what Micron's stock does on Monday.

"If trading opens substantially lower it could be the case that a plaintiffs' attorney or two or three will start to conduct an investigation," the broker said.

Trading in Micron shares was halted on Friday morning pending the company's announcement. The shares were down at $7.48 in extended trading, from a last quote of $7.95 on the Nasdaq, before the halt.

(Additional reporting by Himank Sharma in Bangalore, Ben Berkowitz in New York, Writing by Edwin Chan, Editing by Andre Grenon, Gary Hill and Tim Dobbyn)

• A Permanent Economic Emergency