Jack St. Clair Kilby, 81, died of cancer Monday at his home in Dallas, almost 50 years after his idea for what is commonly known as the microchip revolutionized the way that the world computes, calculates and communicates, ushering in the Information Age.

Kilby won the 2000 Nobel Prize in physics for his 1958 invention of the integrated electronic circuit, which made personal computers, satellite navigation systems, cell phones and the $200 billion field of microelectronics possible. He invented the hand-held calculator, which commercialized the microchip, and held more than 60 other patents.

"In my opinion, there are only a handful of people whose works have truly transformed the world and the way we live in it -- Henry Ford, Thomas Edison, the Wright brothers and Jack Kilby," Tom Engibous, chairman of Texas Instruments, where Kilby worked for years, said in a statement. "If there was ever a seminal invention that transformed not only our industry but our world, it was Jack's invention of the first integrated circuit."

Kilby, who failed the college entrance exam for MIT, had not worked at Texas Instruments long enough to merit vacation during the company's annual summer shutdown. So he was alone in the labs, working on borrowed equipment on July 24, 1958, when he struck upon the idea that he jotted down in his notebook: "The following circuit elements could be made on a single slice: resistors, capacitor, distributed capacitor, transistor."

Engineers call that the Monolithic Idea. It cracked a nagging engineering problem. The transistor had been invented 10 years earlier, replacing the vacuum tubes used in the earliest computers. But transistors were built of components strung together with wires. A single bad connection would ruin the circuit, and circuits could only get so small before it was impossible for humans to solder them together. Kilby's idea was to eliminate the wires and use a single block of silicon, or germanium, containing an entire electronic circuit.

When he built the first circuit, it was half the size of a paper clip. In the same space, engineers can now squeeze about 100 million transistors.

The chip first went to work in a computer for the Air Force in 1961 and in the Minuteman missile in 1962. A list of what it's used for today is almost endless: CAT scans, vehicle emission controls, sports broadcasting replays, iPods, military night-vision goggles, microwave ovens and pet-locator devices, among others.

Kilby's invention came just six months before Robert Noyce, who later co-founded Intel Corp., came up with the same idea. Noyce, who died in 1990, was usually credited with making the idea practical, while Mr. Kilby was acknowledged as the first to conceive of the idea of putting components on a single piece of material. After a 10-year patent battle, the men called themselves co-inventors of the microchip, and Kilby publicly credited Noyce in his Nobel Prize speech.

A quiet, self-effacing man, the 6-foot-6 Kilby "seemed almost embarrassed by the attention" of the Nobel Prize, said Washington Post writer T.R. Reid, who wrote a book about the invention. "I never imagined how much human ingenuity could do to turn that one idea into useful applications," Kilby told Reid.

The accolades that came with the Nobel reminded Kilby of the story told by a previous Nobel recipient, Charles Townes, of a beaver gnawing on a branch just below the Hoover Dam.

"Somebody came along and looked at the massive structure and said, 'Did you build that thing?' And the beaver answered, 'Well, it's kind of based on an idea of mine,' " Kilby said.

Kilby was born in Jefferson City, Mo., and grew up in Great Bend, Kan. During World War II, he was in the Army and was sent to India, where his job was to repair radios, although there were no spare parts. The resourcefulness that the assignment taught him proved useful later in his life.

After the war, he took the MIT entrance exam but fell three points short of the required grade. He enrolled in the University of Illinois and graduated with a degree in electrical engineering, then received a master's degree in electrical engineering from the University of Wisconsin in 1950.

He worked for Globe Union, a Milwaukee firm, for 10 years before taking a job at Texas Instruments in Dallas. He became an independent consultant in 1970 and officially retired during the 1980s, but he continued to drop in at Texas Instruments to inspire younger engineers. He was a professor of electrical engineering at Texas A&M University from 1978 to 1984.

Some controversy attended his Nobel Prize. Kilby was not a physicist, and some research scientists felt that his invention ventured perilously close to mere applied science and away from fundamental science. The Nobel committee decided, however, to honor inventions related to the tech world; Kilby shared the prize with Zhores I. Alferov and Herbert Kroemer, who developed electronic components that turned solid-state lasers into practical devices, such as bar-code scanners.

Kilby preferred the title of engineer to scientist, saying that scientists get ideas but engineers make them work. He invented a wide variety of electronic gadgets. At his wife's suggestion, he created a precursor to the telephone answering machine: a device that screens telephone calls so the phone won't ring unless the call is one you want to take. He spent several years developing a household solar-energy generator.

The awards piled up: He was given the National Medal of Science in 1970 and named to the National Inventors Hall of Fame in 1981. In 1989, the National Academy of Engineering gave Kilby and Noyce its top award. In 1995, he received the Robert Noyce Award from the Semiconductor Industry Association. The Institute of Electrical and Electronic Engineers gave him its fellow title and its medal of honor. Japan gave him its Kyoto Prize for the betterment of mankind.

His wife of 34 years, Barbara Louise Annegars, died in 1981. His sister, who cared for him, died in December. Survivors include two daughters and five granddaughters.

Although Kilby's work inaugurated the Information Age, he was slow to embrace the latest consumer technologies and worked on outdated computers for years. He didn't own a digital watch or a cell phone as recently as a year ago. He preferred a slide rule but would use his own hand-held calculator because of its greater accuracy.

Kilby was once asked what the worst application of his invention was. His response was immediate: the singing greeting card.

Jack Kilby, shown in 1982, invented the integrated electronic circuit -- the microchip.