Hoping to become the first American male to win a grand slam tournament since he won at Flushing Meadows in 2003, Roddick blasted 17 aces and successfully landed 72 percent of his first serves to subdue Hewitt.
"He came out serving so well at the start," said Hewitt, the 2001 Open champion. "So you're sort of up against it right from the word 'go'.
"He didn't give me too many opportunities the first few service games to get into points, give me too many looks at second serves."
Ninth seed Roddick will now face unseeded Mikhail Youzhny of Russia, who shocked second seed Rafael Nadal 6-3, 5-7, 7-6, 6-1 in their quarter-final.
Hewitt entered the match with a 6-2 record against Roddick, including 3-0 in grand slams.
"I competed well," said Roddick. "I didn't panic, which is maybe what I've done against Lleyton at slams a couple times before, most notably in Australia (in 2005) when I lost to him there. I didn't play myself out of points.
"I was down a couple break of points in the third set and a break point in the second set, and just was patient and try to make him come up with the goods as opposed to forcing.
"I did a good job of waiting for my shot, and then when it came, pulling the trigger."
Roddick had 46 winners and only 19 unforced errors against Hewitt to win the match in under two hours. He returns to the Open semi-finals for the first time since he won it three years ago.
"I feel like I'm hitting every serve pretty confidently right now," said Roddick. "Maybe sometimes when you feel like you're not getting good slice on it or you're not hitting your kick that well, then you have to go to the fastball a little bit more.
"I feel like there are options are available to me right now."
Hewitt said when Roddick is "serving well, he's obviously tough to beat."
"He had great serving rhythm the whole match," said Hewitt. "There were really very few points that I got opportunities."
