A semiconductor device with improved reliability is provided. The semiconductor device in a QFN package configuration has a semiconductor chip mounted on a tab, leads which are alternately arranged around the tab and electrically connected to the electrodes of the semiconductor chip via bonding wires, and an encapsulating resin portion for encapsulating therein the semiconductor chip and the bonding wires. The lower exposed surfaces of the leads are exposed at the outer peripheral portion of the back surface of the encapsulating resin portion to form external terminals. The lower exposed surfaces of the leads are exposed at the portion of the back surface of the encapsulating resin portion which is located inwardly of the lower exposed surface of the leads to also form external terminals. The cut surfaces of the leads are exposed at the cut surfaces of the encapsulating resin portion, while the upper exposed surfaces of the leads are exposed from the portion of the encapsulating resin portion which is proximate to the cut surfaces thereof. Each of the upper exposed surfaces of the leads has a width smaller than the width of each of the lower exposed surfaces thereof.