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. A
large holding capacitor Cs is not provided in the pixel portion but, instead, the
channel length and the channel width of the driving TFTs are increased, and the
channel capacitance is utilized as Cs. The channel length is selected to be very
larger than the channel width 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. In the case of the 3-transistor pixels, the switching
TFT and the erasing TFT are linearly arranged to further increase the aperture ratio.
