The present invention provides a method of manufacturing an electric device, wherein an adhesive applied on a flexible wiring board is heated to a first temperature to lower its viscosity to a sufficient level, after which a semiconductor chip is placed onto the adhesive at a preset location, so that no air is trapped in the adhesive. The adhesive is heated to a second temperature higher than the first temperature in a permanent bonding step to increase its viscosity, whereby any remaining voids are removed with residual adhesive being pushed aside. Having no voids in the adhesive, the resultant electric device is highly reliable in respect of conductivity.