An Ensemble Monte Carlo (EMC) approach to simulate electron transport in InP surface layers. The EMC includes scattering caused by surface roughness, ionized impurities, defects, and polar optic and acoustic phonons. The EMC has been used to analyze two different ranges experiment mobility measurements reported in the literature. Low mobility samples with weak temperature dependence are dominated by surface roughness and ionized impurity scattering. Polar optic scattering at moderate electrical fields is shown to have a strong influence on high mobility samples.