The medical examiner's office identified the man on Monday as 36-year-old Peter Hass of Orinda.
Hass collapsed toward the end of the 13.1-mile Kaiser Permanente San Francisco Half Marathon. The race drew 10,000 participants Sunday, as temperatures hit an unseasonably warm 77 degrees in the city.
Witnesses told the San Francisco Chronicle that runners and spectators began performing CPR on Haas when no medical staff immediately arrived. The Chronicle reports that ambulances also were delayed because fire dispatchers were given three different locations for the incident.
RhodyCo Productions, which produced the race, did not immediately respond to requests for comment.
The medical examiner says the cause of death is still unknown.