(Reuters) - Tesla Inc was set to breach $500 billion in market value on Tuesday, as its shares extended a meteoric rally that has seen the stock gain more than six times this year.

Shares of the electric-car maker have risen nearly 28% since the S&P Dow Jones Indices confirmed they would add the company to Wall Street’s benchmark index from Dec. 21.

Its shares were up 3.5% at $540.53 in premarket trading and will have to open above $527.48 to hit the $500 billion mark.

The recent rally has also boosted Chief Executive Officer Elon Musk’s net worth by $7.2 billion to $127.9 billion, helping him go past Bill Gates to become the world’s second-richest person, according to the Bloomberg Billionaires Index.

Tesla has become by far the world’s most valuable automaker, despite a production that is a fraction of Toyota Motor Corp, Volkswagen AG or General Motors Co.

Shares of other electric vehicle (EV) makers have also risen in the last few months as President-elect Joe Biden made boosting EVs a top priority during his campaign.