Changes in sheet resistance of n- and p-type InGaP exposed to Electron Cyclotron Resonance Ar plasmas have been used to measure the introduction of ion-induced damage. P-type material is much more resistant to change in its conductivity than n-type InGaP, indicating that electron traps are the predominant entity produced by the ion bombardment. For short (˜1 min.) plasma exposures the ion current is more important than ion energy in producing resistance changes. Annealing of damage in both conductivity types occurs with an activation energy of ˜3.4±0.5eV. p+A1GaAs is found to be much more susceptible than n+AlGaAs to the introduction of electrically active deep levels during exposure to Electron Cyclotron Resonance Ar plasmas. In both AlGaAs materials the resistivity of thin (˜0.5μm) epitaxial layers increases rapidly with both plasma exposure time and the ion energy, while the ion density in the Ar discharge has a much greater influence on p+AlGaAs than n-type material. These results suggest that the energetic ion bombardment introduces deep hole traps more readily than deep electron traps in AlGaAs and that pnp transistor structures will be more susceptible to plasma damage than comparable npn structures.