"The board's decision to appoint Barbara as chairman is a reflection of her leadership and substantial contributions to the company's operating and financial performance since joining the company in 2011," said lead director Richard Kelson in a statement. 

"The appointment will also promote unified leadership for the company, allowing for a single, clear focus for management to execute its strategy and business plans," he said. 

The appointment takes effect 11 January 2018. Smith has been a board member since September, when she was promoted as chief executive. She is succeeding chairman and former chief executive Joe Alvarado, who is retiring.