The United States easily managed the 25-14, 25-21, 25-22 sweep without captain Lindsey Berg, who injured her left ankle in the team's final preliminary round match against Turkey on Sunday. Courtney Thompson started in her place as setter.
"It was great, I had fun and I was thankful," said Thompson, who is playing in her first Olympics. "My teammates are amazing."
Destinee Hooker, who scored 19 points for the United States, said "Courtney's a quarterback.
"She went out there and took control of the game," she added. "She knows our rhythm and it was great to have her on the court."
Coach Hugh McCutcheon said Berg's injury is day to day, but was impressed by her replacement.
"I thought Courtney did a great job," he said. "I don't think we missed too many beats tonight."
Often during timeouts, Berg would pull her aside to confer. The 27-year-old Thompson helped the Americans to a bronze medal at the 2011 Pan American Games, including the four-set win over the Dominicans.
The top-ranked U.S. team, with six straight victories, will play the winner of Tuesday's late match between Italy and South Korea. The other semifinal Thursday was set when both Japan and Brazil won their quarterfinal matches earlier in the day.
The Americans have never won a gold medal in indoor volleyball. The team fell just short at the Beijing Games, taking home the silver after falling in the final to Brazil.
Now, playing under McCutcheon, who led the U.S. men to the gold in Beijing, the United States is among the favourites in the tournament.
The Americans took over top spot in the world rankings at the end of 2011, ending Brazil's four-year run at No. 1. The women qualified for the Olympics in November with a silver-medal finish in the FIVB World Cup.
The U.S. beat No. 2 Brazil 3-1 in a preliminary-round rematch of the Beijing final last week.
The 11th-ranked Dominican Republic finished 2-3 in pool play, beating both Algeria and Britain in straight sets. The Dominicans' only other Olympic appearance was at the Athens Games, where they upset the United States 3-2 but finished in 11th.
The Americans have defeated the Dominican Republic three times this year, most recently in a four-set semifinal match at the Pan American Cup.
The United States jumped out to a 12-3 lead and rolled through the first set, winning it on Foluke Akinradewo's block.
While clearly overmatched, the Dominican Republic took an 8-6 lead in the second set on Candida Estafany Arias Perez. The United States regained the lead when Hooker's spike made it 11-10.
The Dominicans denied the U.S. set point three times, but Jordan Larson eventually spiked to win it.
The U.S. took an 18-12 lead on Christa Harmotto's spike, but the Dominicans closed to within 19-18 before the Americans won it on Bethania de la Cruz de Pena's misplayed kill.
Prisilla Altagracia Rivera Brens finished with 15 points for the Dominican Republic.
The entire Dominican team attended the post-match news conference, many of them crying, to honour captain Milagros Cabral del la Cruz, who is retiring.
"This is a very young team who played against one of the best teams in the world at a very high level," Cabral de la Cruz said.
Earlier Tuesday, defending champion Brazil denied Russia match point six times before winning 3-2 to earn a spot in the semifinals.
The Brazilians will face Japan, which used finesse to counter strength in a 3-2 victory over China.