The university said in a statement that Koch died Sunday at his Hadley home. He was 59.
Koch had a 222-182-45 record in 23 seasons at UMass. He won four regular-season Atlantic 10 Conference titles and two A-10 tournament championships, reaching the NCAA tournament three times.
In 2007, the unranked Minutemen won four consecutive games, including 2-1 against No. 1 Boston College, to reach the tournament's final four, before losing 1-0 to Ohio State in the semifinals.
Before UMass, Koch was the coach at Stanford from 1984-89, going 58-53-16.
He is survived by his wife and four children.