An additional seven officers were suspended without pay, and another is receiving counseling, according to
CNN affiliate KRON4.
The four Oakland Police Department officers who were terminated also face charges of attempted sexual assault, lewd conduct in public, assisting in the crime of prostitution, being untruthful to investigators, and failing to report a violation of law for not disclosing that a minor had sexual contact with police.
The seven suspended officers are accused of accessing a law enforcement database for personal gain, failing to report a violation of the law, and bringing disrepute to the department.
Schaaf said at the press conference that the firings and suspensions send "a loud and clear message that we hold our officers to nothing but the highest standards of professionalism and integrity."
The punishments bring some resolution to the scandal that began last fall with the suicide of OPD officer Brendan O'Brien. Officials say an investigation into his death uncovered disturbing allegations.
An 18-year-old former prostitute alleged she had sex with O'Brien, as well as with a number of other officers from the department and officers from nearby jurisdictions.
The young woman, who goes by the pseudonym Celeste Guap, said it all started when she was 17 years old and became romantically involved with O'Brien, who she credits with saving her from a dangerous pimp.
"He saved me when I was 17," Guap told CNN in a phone conversation. "Instead of taking me to jail, we just kind of started something there, you know."
O'Brian, she said, later introduced her to other officers who became customers.
As the investigation widened, other officers became embroiled in the scandal. Ultimately, four police chiefs resigned and 28 officers across five departments were alleged to have had sexual contact with Guap.
Some of the officers paid to have sex, Guap said. Others exchanged confidential information, such as tipping her off about prostitution stings, for sexual favors.
Of the 28 officers, Guap said 14 were from the Oakland Police Department. The others included five Richmond police officers, several Alameda County Sherriff's deputies, a Livermore police officer and a Contra Costa County Sheriff's deputy.
The Oakland Police Department is no stranger to scandal. Since 2003 a federal monitor has been in place to ensure the department complies with a negotiated settlement agreement stemming from a police corruption scandal.
Officers had been accused of planting evidence and assaulting suspects. No accused officers were ever convicted, but one officer fled prosecution and to this day remains at large. The city paid out more than $10 million to more than 100 plaintiffs and agreed to make reforms, eventually ending up under federal monitoring.
Wednesday's announcements were "about making department-wide changes," Schaaf said.
"We see you, we are here for you, we are here to help you," she added, addressing victims of sexual abuse in the city.