The cutoff frequency ft and maximum frequency of oscillation fmax of the permeable-base transistor have been calculated for devices with a fixed geometry and different doping profiles to determine the profile that gave the highest value of fmax The effect of different static velocity-field curves for GaAs and InP, and associated diffusion-field dependencies on device performance have also been examined. The results of the simulations show that the saturated velocity for GaAs PBT's has a major impact on performance. The uniformly doped device, Ndof 4 x 1016 cm-3, has a higher fmax when the saturated velocity is larger, but the effect of the low field mobility is small. The InP device has a slightly higher fmax than the corresponding GaAs devices at this doping level. The 20-10-4 x 1016cm-3 devices have the highest fmax of all the GaAs devices investigated.