European Games champion Bennama beat Yunior Alcantara of the Dominican Republic by unanimous decision, before Rio Olympics silver medallist Oumiha clinched a hard-fought 4-1 win over Canada's Wyatt Sanford in the very next bout.
China's Asian Games and world champion Li Qian triumphed in a middleweight quarter-final against Tokyo Olympics bronze medallist Lovlina Borgohain of India, taking a 4-1 win to become the fifth woman from the country to ensure a medal at this Games.
Li's compatriot and former Asian Games champion Chang Yuan was also victorious, beating North Korea's Pang Chol-mi on a 3-2 split decision to progress to the final of the bantamweight category.
"She is a great rival, we have faced each other many times and I have learned a lot from facing her. I wanted to take those learnings and be better today. A lot of times when you lose, it's usually down to yourself," Chang said.
"Today, I won because of how sure I was in executing my strategy, whether it's in the strength of my punches or others."
Australia, who arrived at the Games with the largest contingent of boxers (12) but have just two representatives left standing, scored a win in the women's middleweight quarter-finals when Caitlin Parker beat Moroccan Khadija Mardi 4-1.
Parker's win saw her move into the semi-finals and become the first Australian woman to win a boxing medal at the Olympics.
"I can't wait to call mum and dad and scream on the phone honestly," the 28-year-old said.
"It's mindblowing. Watching Charlie Senior secure our first medal yesterday (by winning his quarter-final), I was in absolute bloody tears, and then he came back to the Olympic Village and we just cried together.
"It was just an incredible moment. That pumped me up so much and I felt that I had to bring everything (to her quarter-final), and I did that. I will probably not sleep tonight, just smiling and looking at the roof."
In a clash between two Cuban boxers who are now representing different nations, Azerbaijan's Loren Alfonso beat Spaniard Enmanuel Reyes 4-1 in a heavyweight semi-final.
