Previous research has indicated that modeling evapotranspiration (ET) in the Arctic Coastal Plain is challenging due to unique ecosystem conditions which include mosses, permafrost, and standing dead vegetation. A new version of the commonly used Biome–BGC (Biogeochemical Cycles) model (Arctic Biome–BGC) was developed that included: (1) a water storage and vertical drainage/infiltration routine that accounts for permafrost and mosses, (2) a modified representation of energy available at the surface which includes ground heat flux and simulates interception of incoming radiation by standing dead vegetation, and (3) a background evaporation routine that allows for moss and open water evaporation. In this study we investigated the sensitivity of model predictions to variations in parameter values, and to provide a conceptual validation of Arctic Biome–BGC. Using the generalized sensitivity analysis methodology, 13 parameters were evaluated. Results indicate that the model was sensitive to 8 of the 13 parameters. Seven of these parameters were introduced in the development of Arctic Biome–BGC and related to both energy reaching the ground surface and the amount of water stored within the soil and moss layers. The remaining sensitive parameter modulates the rate of snowmelt. These results validate the conceptual modifications included in the Arctic Biome–BGC model for estimating ET.