Billionaire Elon Musk has offered to buy Twitter for about US$41 billion, just days after rejecting a seat on the social media company’s board.

Musk’s offer price of US$54.20 per share, which was disclosed in a regulatory filing on Thursday, represents a 38 per cent premium to Twitter’s April 1 close, the last trading day before the Tesla CEO’s more than nine per cent stake in the company was made public.

Twitter’s shares jumped 12 per cent in premarket trading.

“Since making my investment I now realize the company will neither thrive nor serve this societal imperative in its current form. Twitter needs to be transformed as a private company,” Musk said in a letter to Twitter Chairman Bret Taylor.

“My offer is my best and final offer and if it is not accepted, I would need to reconsider my position as a shareholder,” Musk said.