We study the effect of non-ideal surface conditions on the characteristics of submicrometer type-II InP/GaAsSb double heterostructure bipolar transistors (DHBTs) by comparing two-dimensional numerical simulations with measured device characteristics. The inclusion of surface effects in simulations enables excellent agreement with measured Gummel characteristics and measured emitter size effects, and shows that recombination at the emitter mesa periphery on the extrinsic base surface is the major source on non-ideality in device characteristics. The simulations also demonstrate that AlInAs emitters should result in weaker surface recombination and emitter size effects. (C) 2007 Elsevier Ltd. All rights reserved.