Header leads in a molded semiconductor device according to this invention are composed of electrode portions for securing a semiconductor pellet, and lead portions for connection. Each of the electrode portions is constructed of two tabular header portions separated from each other, and a columnar neck portion coupling both the header portions between opposing surfaces thereof. The lead portion is joined to one of the tubular header portions so that the lead portion and the columnar neck portion may extend coaxially. The cross-sectional area of the columnar neck portion in a direction orthogonal to the direction of the axis is larger than the cross-sectional area of the lead portion in the orthogonal direction. The semiconductor pellet is secured to the other header portion of each electrode portion. A mold material covers the entire periphery of the device from the semiconductor pellet to the one header portion of the electrode portion.