Pnp InP/InGaAs heterojunction bipolar transistors have been modeled using a modified Gummel-Poon model, and the results are compared with experimental measurements and results from a commercial simulator. The model provides a good description of the transistor's high frequency performance and describes the falloff in device performance at high current densities. The model overestimates the current gain at low current densities by neglecting hole recombination in the base side of the emitter-base space charge region.