The quantum barrier semiconductor optical devices according to this invention are characterized by strained layer super lattice multiple quantum barriers provided between active layer and p-clad layer or within p-clad layer to obtain resonance scattering of incident overflowing electrons, that is to realize phase condition in which the incident overflowing electron wave and reflected electron wave enhance each other, in the double heterostructure where active layer having at least one GaInAs(P) layer is sandwiched between n-clad layer and p-clad layer. In this case, the active layer should desirably have quantum well structure. The quantum barrier semiconductor optical device comprises a DCCtype double heterostructure made by growing an n-clad layer, a fist active layer having at least one GaInAs(P) sub-layer, a middle clad layer, a second active layer having at least one GaThAS(p) sub-layer, and a p-clad layer in the order of mention or vice versa and a super lattice resonance scattering type quantum barriers provided between the first active layer and middle clad layer or in the middle clad layer and/or between the second active layer and p-clad layer or within p-clad layer. In this case also, the active layer should desirably have quantum well structure and the quantum barriers should desirably be made up of strained layer super lattice.