A wideband steady-state numerical model of a tensile-strained bulk InGaAsP semiconductor optical amplifier (SOA) is presented. The model is based on a set of travelling wave equations that govern the propagation of the amplified signal and spontaneous emission photon rates and a carrier density rate equation. The model is applicable over a wide range of operating regimes and can be used to determine the effects of varying the amplifier geometric and material parameters. Simulations and comparisons with experiment are given which demonstrate the versatility of the model. © Springer Science+Business Media B.V. 2007.