The present invention provides a display device of high quality by suppressing heating of a semiconductor chip mounted on a flexible board connected to an insulation substrate of a display device and by suppressing irregularities of a voltage supplied to the semiconductor chip. A heat radiation pattern is formed on a flexible board which is connected to the insulation substrate of the display device and mounts a semiconductor chip thereon. By connecting heat radiation bumps of the semiconductor chip and the heat radiation pattern, heat generated from the semiconductor chip is dissipated by the heat radiation pattern. Further, by supplying a predetermined voltage to the semiconductor chip via the heat radiation pattern and the heat radiation bumps, the irregularities of an input voltage tothe semiconductor chip can be also suppressed.