George Doodnaught was accused of kissing, fondling and forcing oral sex on the patients at North York General Hospital in Toronto during a four-year period that ended in 2010.
The victims were aware of what was happening but could not move, the court heard.
The defense argued that the victims actually had vivid sexual dreams caused by sedatives known to play tricks with memory, and that Doodnaught could not have assaulted them undetected by others separated only by a surgical screen in the operating room.
A researcher confirmed at trial that the drugs can cause hallucinations.
But he added that it is unlikely that all of the women, who did not know each other, would come forward separately with similar accusations against the same doctor.
The prosecution said Doodnaught was an experienced doctor who knew the routines of a busy operating room, and timed the brief assaults to avoid detection.
"He had control over their level of anaesthesia and would have known that they could not openly resist," Ontario Superior Court Judge David McCombs said in his ruling.
"He relied on the amnesiac effects of the drugs to shield him from complaints."
Doodnaught is scheduled to return to court next month to set a date for sentencing.