Technical Abstract: Estimating the distribution of the energy balance components under different surface conditions is important to better understand the contribution of these fluxes in the hydrologic cycle. The latent heat flux, or evapotranspiration, is the largest component of the hydrologic fluxes after precipitation. However its estimation in partially vegetated, semi-arid ecosystems is still the subject of much study due to the complex nature of the problem. Existing evapotranspiration models are hindered in representing vegetation parameters that influence transpiration in highly heterogeneous ecosystems. This paper briefly describes a distributed energy balance model developed for semi-arid, complex terrain with sparsely vegetated ecosystems. The development objective was to model the energy balance process in a distributed manner in order to better understand the mechanisms that control the partitioning of energy in environments with sparse vegetation and limited water availability. The model was applied to a semi-arid mountainous sub-basin of the USDA-ARS Reynolds Creek Experimental Watershed, near Boise, Idaho.