This paper presents a semi-empirical approach based on charge sheet model of Poly-Si TFT, valid in all regions to explain the electrical characteristics of a new Poly-Si TFT structure having an air-gap of thickness 50 nm just below the channel region. The model predicts the output as well as the transfer characteristics of the device for various grain sizes. The presence of air-gap aims at increasing the effective field dependent mobility which eventually drastically improves the current driving capability and the performance of the device. The theoretical results have been compared with the experimental data to validate the present approach. (C) 2005 Elsevier Ltd. All rights reserved.