We utilized phase-shifting electron holography on organic light emitting diodes consisting of N,N′-di-[(1-naphthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (α-NPD) and tris-(8-hydroxyquinoline)aluminum (Alq 3 ) layers to visualize their built-in potential distribution. The bilayer showed three different electric fields, namely, the fields in the α-NPD layer, near the α-NPD/Alq 3 interface, and in the Alq 3 layer measured as −1.8 ± 0.4 MV m −1 , −10.0 ± 2 MV m −1 , 3.1 ± 0.6 MV m −1 , respectively. We show that they are related to hole accumulation in the α-NPD layer, the charge carrier accumulation junction around the α-NPD/Alq 3 interface, and the giant surface potential spontaneously polarized in the Alq 3 layer.