NEW YORK (REUTERS) - Apple became the first US company to top the US$800 billion (S$1.1 trillion) mark in market capitalisation on Tuesday, slightly more than two years after it crossed the US$700 billion threshold.

The iPhone maker's shares have gained 33 per cent this year and almost 50 per cent since the US election in November.

The company represents about 4 percent of the US$21.7 trillion that makes up the entire S&P 500 index.

Apple accounted for as much as 4.9 per cent of the S&P 500 in September 2012 but is a smaller percentage now as the index as a whole has rallied more than 7 per cent this year.

"It's just reflective of how powerful a franchise it is. It may be the most powerful franchise in the country today," said Rick Meckler, president of LibertyView Capital Management in Jersey City, New Jersey, whose firm does not own the stock.

"Considering that it has a limited number of products, it has really dominated that market in a way that few companies have, and it's been able to retain margins despite lots of competitors."

If Apple continues on its growth path, the company will top the US$1 trillion market cap level later this year.

Stock buybacks have also bolstered Apple shares, with the company reducing its actual share count by 20.9 per cent and the average diluted shares outstanding by 20.5 per cent over the past four years, according to Standard & Poor's data.

The median price target on Apple is US$160, up from the US$140 median three months ago. Shares closed at US$153.99 on Tuesday.

The closing market cap of US$802.8 billion was larger than the economies of 45 of the 50 US states, topped only by Illinois, Florida, New York, Texas and California.

Billionaire Warren Buffett, whose Berkshire Hathaway has disclosed a stake of roughly US$20 billion in Apple, said on Monday he had grown more fond of the company because he could "very easily determine" the iPhone maker's competitive position "and who is trying to chase them."