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In this study, common algorithms of land surface energy balance (EB) methods used to estimate actual evapotranspiration (ETa) were evaluated using meteorological data in combination with reflectance measurements obtained by a hand-held multi-spectral radiometer over a drip-irrigated 'Merlot' vineyard trained on a vertical shoot positioned system (VSP) under semi-arid conditions. The vineyard is located in the Talca Valley, Maule Region, Chile, and data used in this study (21 days) were collected during two consecutive growing seasons (2007/2008 and 2008/2009) at different phenological stages. The performance of the EB algorithm used to estimate the components of the surface energy balance was evaluated by the eddy covariance system (EC), net radiometer and soil heat flux plate measurements. The estimated values of ETa of the vineyard plot showed a good agreement with ETa values derived from EC measurements, with a root mean square error (RMSE) and a mean bias error (MBE) of 0.32 and 0.09 mm day(-1), respectively. These results validate the potential use of a hand-held multi-spectral radiometer for estimating instantaneous evapotranspiration (ETa ins) and its extrapolation to ETa.