Microsoft co-founder Bill Gates has retained his number one position in the Forbes’ annual list of the “richest people in America” for the 19th consecutive year.

Gates (56), a Harvard dropout with a net worth of $66 billion, is the wealthiest American on the list of the nation’s 400 super rich who have a combined net worth of $1.7 trillion.

The top five richest in the list remain unchanged from the previous year while there are 20 new entrants to the top 400 list, according Forbes. They include Laurene Powell Jobs, widow of Apple co-founder Steve Jobs, who is also the fifth richest women in the U.S.

Gates’ philanthropic activities in several countries has also got him the title of the “planet’s most generous person.” He has donated $28 billion for philanthropic causes so far and his net worth has increased by $7 billion since August last year as the Microsoft shares climbed 20 percent during the period and the billionaire also gained from investments in private equity, bonds and stocks, according to Forbes.

Warren Buffett, chairman of Berkshire Hathaway, is the second richest American on the list with a net worth of $ 46 billion. Buffett (82) has contributed $17.25 billion so far to philanthropic endeavors.

Larry Ellison, chief executive officer of Oracle Corp., is in the third spot with $41 billion while 76-year-old Charles Koch, head of Koch Industries with $31 billion and 72-year-old David Koch, executive vice president of chemical technology for Koch Industries, stood at fourth and fifth position s respectively.

The number of women who have made it to the list also rose to 45 from 42 in the previous year, Forbes said.

The notable fall on the list is of Facebook co-founder and CEO Mark Zuckerberg, who slipped from the 14th position with a fortune of $17.5 billion in 2011 to 36th position with $9.4 billion net worth. His fortunes nearly halved after the Facebook IPO fiasco and a fall in the social media businesses.

The combined net worth of the 2012 class of the 400 richest Americans is $1.7 trillion, up 13 percent from the $1.5 trillion a year ago, according to Forbes.