We have investigated the growth, interface structure, and magnetic properties of full-Heusler alloy Co2FeSi/GaAs(0 0 1) hybrid structures. We found that a L2(1)-ordered Co2FeSi layer with an atomically abrupt interface can be achieved up to the growth temperature T-G of 200 degrees C. The simulations of the high-resolution transmission electron microscopy interference pattern for Co2FeSi/GaAs(0 0 1) interface suggests a I layer of intermixing at the interface. Both uniaxial and cubic in-plane magnetic anisotropy constants decrease above 200 degrees C in correspondence with the proceeding interfacial reaction, indicating degradations of the interface perfection as well as the ordering of the layer. The formation of interfacial compounds reduces the saturation magnetization of the Co2FeSi layer in higher T-G, which can deteriorate its expected half-metallicity. (c) 2006 Elsevier B.V. All rights reserved.