This paper is aimed at giving the basic knowledge of the organic thin film transistors. To start with basic knowledge of different structures of single gate OTFT has been provided. Thereafter the simulation of BGBC single gate OTFT has been done and the results are shown. Finally the simulation of dual gate OTFT has been done and the results are shown. These two different structures have then been compared based on their performance parameters like threshold voltage, sub-threshold slope, mobility, current ratio. It is seen that the performance of DG-OTFT is better that the single gate OTFT in all the spheres because of the extra gate that has been added. Thus the DG_OTFT devices are more robust and have better performance.