At about 1:30 a.m., officers responded to the Piedmont Hiills neighborhood of east San Jose.
They arrived at a home in the 3400 block of Suncrest Avenue to find a man suffering from at least one stab wound.
Witnesses say a fight broke out at a 21st birthday party. The hosts asked everyone to leave. That's when another fight started outside the home.
"And then my niece's boyfriend tried to break up the fight," Paul Pham said. "That's what I heard from my brother. And so he tried to break up the fight, somehow got stabbed right here. I heard he died."
Paramedics took the victim to a local hospital where he died a short time later.
The victim's name has not been released. Police have also not named a suspect yet.
This is the city's fourth homicide of 2014.