A-light-emitting device which realizes a high aperture ratio and in which the quality of image is little affected by the variation in the characteristics of TFTs. The channel length of the driving TFTs is selected to be very larger than the channel width of the driving TFTs to improve current characteristics in the saturated region, and a high VGS is applied to the driving TFTs to obtain a desired drain current. Therefore, the drain currents of the driving TFTs are little affected by the variation in the threshold voltage. In laying out the pixels, further, wiring is arranged under the partitioning wall and the driving TFTs are arranged under the wiring in order to avoid a decrease in the aperture ratio despite of an increase in the size of the driving TFT.