Another 17 are still missing.
Abdul Muhari, the spokesman for the disaster mitigation agency, said the disaster forced nearly 3,700 people to evacuate and damaged nearly 3,000 houses and 38 schools.
Ash spewed from the volcano blanketed Lumajang district in East Java, causing serious air pollution. Residents were advised to stay 5km from the volcano.
Rescue work was made difficult by the pyroclastic flow and rains.
The 3,600m Semeru Mount is among nearly 130 active volcanos in Indonesia. Earlier, it erupted in January, forcing thousands to flee but causing no casualties.