DALLAS — Jack St. Clair Kilby 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 the world computes, calculates and communicates, ushering in the Information Age. He was 81.

His 1958 invention of the semiconductor shrank tons of complex circuitry to the size of a fingernail and enabled the development of personal computers, automated sprinklers, cellphones, microwave ovens and other staples of modern life.

"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," said Texas Instruments Chairman Tom Engibous. "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."

Indeed, sales of integrated circuits totaled $179 billion in 2004, supporting a global electronics market of more than $1.1 trillion, according to Texas Instruments.

Over his career, Mr. Kilby earned more than 60 patents and was honored as one of the seminal inventors of the 20th century. In addition to the Nobel Prize for Physics in 2000, Mr. Kilby won the National Medal of Science and was inducted into the National Inventors Hall of Fame.

Despite the widespread changes spawned by his invention, he avoided many of the byproducts of his idea. He didn't own a digital watch or a microwave oven. A conventional watch with its sweeping hands better conveyed the passage of time, he reasoned.

And, although he invented the handheld calculator in 1965 to demonstrate a practical use for his semiconductor, Mr. Kilby continued to use his slide rule.

Mother of invention

Desperation was the mother of his invention, if not the catalyst.

The 34-year-old engineer moved to Dallas from Milwaukee, wanting to work on what engineers referred to as the "tyranny of numbers." A computer made of conventional electronics would require tens of thousands of components with up to hundreds of thousands of interconnections. Such computers were limited by size, weight and cost.

Engineers were working on what they called the Monolithic Idea: a single block of semiconductor material containing an entire electronic circuit.

In Dallas, Mr. Kilby, who already had a dozen patented inventions under his belt, hoped to work on the problem with a larger organization, Texas Instruments. But the company was pursuing a different tack than he would have chosen.

While most of Texas Instruments was on summer vacation, Kilby, too new to be eligible for vacation, worked alone in the lab.

"I felt it likely that I would be put to work on a proposal for the Micro-Module program when vacation was over unless I came up with a good idea very quickly," he said in T.R. Reid's book "The Chip."

Problem solver

Mr. Kilby said he simply looked for a solution to the industry's problem. Since Texas Instruments was heavily committed to silicon for transistor production, he focused on using that material.

His solution cracked a nagging engineering problem. The transistor had been invented 10 years earlier, replacing the vacuum tubes of 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.

Mr. 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.

Robert Noyce, co-founder of chip giant Intel, is credited with developing the manufacturing process that made economical the wide-scale production of integrated circuits. Mr. Kilby and Noyce bickered for years over the other's claim to have invented the integrated circuit. Ultimately, the two agreed to share credit.

Recognition

In 1995, Mr. Kilby was awarded the Robert N. Noyce Award, the Semiconductor Industry Association's highest honor. And five years later, when Mr. Kilby won the Nobel Prize, he invited Intel's other founder, Gordon Moore, to the ceremony as a gesture to the contribution of Noyce, who died in 1990. Nobel Prizes are not awarded posthumously.

Unlike Noyce and Moore, Mr. Kilby never shared in the phenomenal wealth created by the microchip.

But, he said, "I don't feel mistreated in any way. It's not possible for one person to create a success like the integrated circuit. Many people are involved in that. Today, tens of thousands of people are still contributing to it."

Jack St. Clair Kilby was born in Jefferson City, Mo., on Nov. 8, 1923, and grew up in Great Bend, Kan.

His father ran a small power company with customers scattered across rural western Kansas. When the young Kilby was in high school, a severe ice storm took down telephone and power lines, and his father worked with amateur radio operators to communicate with his customers.

That sparked Mr. Kilby's lifelong fascination with electronics and helped him decide to become an engineer.

MIT reject

After failing the Massachusetts Institute of Technology admission test by three points, Mr. Kilby attended the University of Illinois, interrupted by serving in the Army in World War II, graduating in 1947 with a degree in electrical engineering. In 1950, he earned a master's degree in electrical engineering from the University of Wisconsin.

In the years after his invention, Mr. Kilby moved through various jobs at Texas Instruments but found he had no taste for management.

He took a leave from the company in 1970 to research topics that interested him and taught at Texas A&M University between 1978 and 1984.

Mr. Kilby retired from Texas Instruments in 1983 but continued to consult with the company, which named its $154 million research complex after him. It also endowed a professorship at the University of Texas at Austin.

Mr. Kilby is survived by two daughters: Janet Kilby Cameron of Palisade, Colo., and Ann Kilby of Austin, Texas.; five granddaughters, and a son-in-law. His wife, Barbara, died in 1981.

Material from the Los Angeles Times, The Associated Press and The Washington Post is included in this report.