PURPOSE: To obtain a semiconductor device which is inexpensive and has high reliability and dimension fitted to the international standard, by leading out external leads from four side surfaces of a package made of synthetic resin at intervals of 50mil.

CONSTITUTION: External leads 2 are led out from four side surface of the plastic package 1 at pitches of respectively 50mil. When the pitch is 50mil, the plate thickness of the lead frame is formed thicker approx. to 0.2W0.25mm in processing than conventional. Since the package is made of plastic, it can be manufactured at a low cost, and since the pitch is 50mil, it is fitted to the international standard, and accordingly the external lead pitch is widened more than in the same type conventional package. Therefore, since the package become large-sized, the distance from the boundary of the lead 2 and the package 1 to the chip pad extends, and the infiltration of contaminating substances is difficult, the reliability is improved.