Marcel Buggs entered his plea in Contra Costa County Superior Court on Tuesday. In addition to three counts of attempted murder, Buggs also is charged with burglary and gang activity.
Prosecutors say Buggs entered the New Gethsemane Church of God in Christ during the Feb. 14 service, scoured the aisles for his victims and then opened fire.
Two brothers -- ages 14 and 19 -- were shot; a third brother escaped uninjured.
Prosecutors say the brothers were targeted because they were North Richmond residents on Central Richmond turf.
Charges have not been filed against two teenage boys suspected of accompanying Buggs inside the church.