Saint Stephen Seminary was a diocesan minor seminary staffed by the Sulpician Fathers in the diocese of Honolulu that closed in 1970. The seminary land was acquired by the Diocese of Honolulu in 1946 and is located at the former 22-acre (89,000 m²) estate of Harold K.L. Castle just above Maunawili valley in the Koolaupoko district of the island of Oahu. The Castle Mansion was built in 1927 and currently serves as the residence of the bishop of Honolulu. The seminary accommodated some 70 high school and college students from Guam, Pacific Islands and the State of Hawaii. After the seminary's closure, the Cullinan Building was transformed into a diocesan center housing various officers of the diocesan curia. Since the episcopate of Msgr. John Scanlan, the seminary grounds have also housed a Carmelite monastery of discalced nuns from Hong Kong.
Currently, candidates for priestly formation in the Diocese of Honolulu attend the metropolitan seminaries of Saint Joseph in Mountain View, California, and Saint Patrick in Menlo Park, California.
Prior to his elevation to the episcopate as auxiliary bishop of Honolulu, Msgr. Joseph Ferrario, was a professor of Greek and Latin at Saint Stephen's. Among his many students was Roman Catholic deacon and Hawaiian comedian, Frank Delima, known for his sardonic portrayal of a fictitious Roman prelate, Monsignor Vermicelli.