Depth profiles of 300‐keV protons implanted inn‐type GaAs at room temperature have been obtained using secondary ion mass spectrometry and correlated with optical effects determined by infrared reflectance measurements. The profiles of the implanted hydrogen (1H) have been measured as a function of annealing for temperatures up to 600 °C. These profiles display a major redistribution of the hydrogen atoms with movement beginning at 200 °C and terminating by 700 °C. The hydrogen diffusion into the substrate can be approximated by an Arrhenius process with an activation energy of 0.62 eV and a diffusion constant of 1.54×10−5cm2/s. The reflectance spectra indicate that while an optically uniform layer is present in the as‐implanted specimen, more complicated optical profiles exist in the annealed samples. Annealing at 300 °C causes the layer to nearly double in thickness but higher temperature annealing produces optical profiles similar to the as‐implanted state. Qualitatively, these optical changes follow the behavior of the hydrogen depth profiles.