PITTSBURGH — A former steel executive-turned-philanthropist who pledged gifts to the University of Pittsburgh and Carnegie Mellon University last month totaling $390 million has died. William S. Dietrich II was 73.

Dietrich’s death was announced today by the John A. Freyvogel Funeral Home. It said he died Thursday but did not disclose the cause.

Dietrich gave $265 million to Carnegie Mellon and $125 million to Pitt in September. The gifts were the largest in the history of each school.

Dietrich, a native of Pittsburgh, was born in 1938. He turned a small family business into the nation’s largest manufacturer of light metal construction framing.