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In drylands, evapotranspiration is mainly limited by soil moisture, but current surface energy balance models do not directly make use of this fact. We tested the single-source energy balance model SEBS in a semi-arid region and showed that SEBS is significantly overestimating the evaporative fraction for sparsely vegetated drylands. As an alternative for such conditions, we derived an empirical function of soil moisture, temperature gradient and NDVI, which performed significantly better. This was then integrated with the evaporative fraction output of SEBS for an improved mapping of evapotranspiration in a semi-arid region. Ground measurements of the evaporative fraction from five Bowen ratio energy balance systems were used first to test SEBS and then to calibrate the empirical equation. The resulting method uses remote sensing data and in situ air temperature measurement.