The present invention provides a semiconductor device which includes a U-shaped metal package base, and a semiconductor chip having at least surface electrodes and being mounted on the inner bottom portion of the U-shaped metal package base, wherein the metal package base has, in a portion thereof ranging from the opened side end portion of the inner side wall to the semiconductor chip, a creep-up preventive zone preventing solder entering from the opened side end portion from creeping up. The device makes it possible to solve problems which have been apprehended for conventional semiconductor devices configured as mounting a semiconductor chip on a small semiconductor package, in that reduction in distance between external terminal portions of the metal package and the semiconductor chip results in contact of a solder for mounting with the semiconductor chip to thereby adversely affect the electrical properties and reliability thereof, and in that resin filling or partial plating for avoiding intrusion of the solder raises the cost.