To provide a thermosetting resin composition having excellent shelf stability at room temperature and excellent curability, and to provide a semiconductor device using the composition.

The thermosetting resin composition is obtained by compounding, as an essential component, a curing accelerator into a thermosetting compound, wherein the curing accelerator is obtained by combining a compound having Lewis acidity with a phosphobetaine compound of an addition reaction product of a tri-substituted-phosphine with a compound having a π-bond preferably conjugated double bond.