Deep proton-isolated (GaAl)As/GaAs lasers have been fabricated in structures where the active layer was 40 μm from the surface. Proton-isolation masks have been made enabling high proton energies, up to 2.5 MeV, to be used. By chemically delineating the proton-bombarded regions studies have been made of proton penetration in (GaAl) As/GaAs laser structures. This work was extended to include a study of proton penetration in other III-V compound semiconductors and results show that the energy-range data for GaAs, InP and GaSb is very similar. The characteristics of deep proton-isolated (GaAl) As/GaAs lasers have been investigated and results are given which show that improvements to the external quantum efficiency, peak power operation and reliability can be realised by using this technique of laser fabrication.