The electrical and optical properties of proton‐bombardedp‐ andn‐type liquid‐encapsulated Czochralski‐grown GaP have been investigated as a function of 300‐keV proton dose and subsequent annealing. Proton bombardment of GaP introduced lattice damage into a surface layer equivalent in thickness to the proton penetration range, and resulted in a large increase in the electrical resistivity, as well as an increase in optical absorption of this damaged surface layer. The thickness of the damaged layer increased linearly with proton energy at approximately 1.0 &mgr;/100 keV in the energy range from 100 to 300 keV. Electrical resistivity in bothp‐ andn‐type samples increased with proton dose to a maximum of ∼1014&OHgr; cm at a dose of 4×1014protons/cm2, and then the resistivity decreased with increasing dose. Optical absorption spectra indicated a continuous distribution of energy levels extending into the band gap. The absorption at 6328 Å (visible red) increased monotonically with proton dose from ∼10% and 1014protons/cm2at 300 keV to ∼90% at 1017protons/cm2. Layers approximately 3.0 &mgr; thick have been produced which have high electrical resistivity (> 1010&OHgr;cm) and relatively low optical absorption (< 10%). The activation energies governing the annealing of the optical and electrical defects are in the range from 2 to 4 eV. The existence of large activation energies for the annealing of bombardment‐induced high resistivity implies high stability near room temperature. This stability combined with ease of forming high‐integrity pinhole‐free layers of controlled thickness on GaP substrates suggests useful applications in the GaP device fabrication technology. Many qualitative similarities have been observed between the proton‐bombarded GaP examined here and the bombardedp‐type GaAs discussed in the previous paper.