Even before "High School Musical 3" hits movie theaters in the fall, Disney Channel is starting work on "High School Musical 4."

Even before "High School Musical 3" hits movie theaters in the fall, Disney Channel is starting work on "High School Musical 4."

"We are writing 'High School Musical 4,'" Disney Channel Worldwide president Rich Ross confirmed yesterday (April 8) after a presentation at a midtown Manhattan recording studio. It's likely to be a TV movie unlike "High School Musical 3: Senior Year," though that could change.

The news comes as the stars of the two smash hit TV movies are preparing for production on the third installment of the series, which will begin filming in two weeks in Utah. There's no word on whether the cast and behind-the-scenes talent will gather again for "HSM4," though some characters introduced in the third go-round likely will star in the fourth.

"Are we going to have all the cast back? Probably not," Ross said. "Will we have some of them? I hope so."

Even for a channel that has international multiplatform properties in "Hannah Montana" and "The Cheetah Girls," among others, "HSM" is big business. The second TV movie shattered cable TV records last summer with a premiere watched by 18.6 million viewers and it has been a hit internationally as well. It boosted Disney Channel to the No. 1 position among cable networks in primetime in 2007.

Ross said that after the original "HSM," he went to Disney Channel entertainment president Gary Marsh and asked whether there was "a new story to tell" in the saga that launched the careers of Zac Efron, Vanessa Anne Hudgens, Ashley Tisdale and Corbin Bleu.

"We have learned that just putting a number next to a title is a very old idea," Ross said. "We have to have a new story."

Marsh answered affirmatively with "HSM2" and later, "HSM3." Now Marsh and Ross are confident that the "HSM4" script is going well.