Actors Jim Parsons, Johnny Galecki and Kaley Cuoco will get big raises for their roles on television sitcom The Big Bang Theory after locking in three-year contracts that will see them earn $1 million US an episode, according to a report on Deadline.com.

The pay increases would be significant for Cuoco, who plays Penny, Parsons (Sheldon Cooper) and Galecki (Leonard Hofstadter).

Previous reports had pegged their earnings at about $350,000 per half-hour episode.

The new contracts would also give the trio a bigger piece of the show's overall profits.

The show, set in Pasadena, Calif., centres on two brilliant but socially awkward physicists (Sheldon and Leonard) whose lives are transformed when an outgoing and attractive waitress (Penny) moves into the apartment across the hall.

In March, CBS renewed the hit series three more seasons, which would bring the show to its 10th year.

Simon Helberg and Kunal Nayyar

Simon Helberg, left, and Kunal Nayyar are said to still be in negotiations, but a deal is expected to be reached this week. (John Shearer/Getty Images)

The ongoing dispute over salaries has delayed production for the show's eighth season, and Warner Bros. Television is reportedly still negotiating with cast members Simon Helberg and Kunal Nayyar

If deals can be reached by Wednesday's production deadline, filming will only be one week behind.

That means fans can still expect the show to return on its slated premiere date of Sept. 22.

Big Bang Theory is the No.1 comedy on television, netting huge ratings for CBS and an estimated $1 billion in profits for Warner Bros.over the next three years.

There has been no official comment from Warner Bros, CBS or representatives of the show's stars.