Exelon boosts offer to acquire NRG by 12 percent

Exelon said NRG common stock holders will receive 0.545 shares of Exelon for each NRG share held, which represents a nearly 8 percent premium above NRG's closing price on Wednesday of $26.05. Exelon said its increased offer represents value of over $3 billion to NRG shareholders.

Shares of NRG Energy were trading 2.88 percent lower to $25.30 a share at the start of trading on the New York Stock Exchange.

"This is our best and final offer, and we will use the time leading up to the NRG annual meeting on July 21 to communicate the value of our new offer to NRG shareholders, encouraging them to vote for nine new independent directors who can unlock that value," Exelon Chief Executive Officer John Rowe said in a statement Thursday.

NRG rejected a previous offering by Exelon - the largest nuclear power company in the U.S. - stating it undervalued the company.

A merger of the two companies will result in the largest power generator in the U.S. and would have the potential to provide electric power to about 45 million households in the country.