thus the cavities 11 formed substantially in the fitting surfaces 3 of the upper and lower mold main bodies 10 and 20 define the shape of the product to be molded each of the cavities 11 for receiving the molding material is provided with a portion 21 for accommodating an excess of the molding material like the cavity 11 the accommodating portion 21 is formed independently in the upper surface of the lower mold main body 20 and communicating with the corresponding cavity 11 through a communicating portion 22 see fig2 lower ejector pins 23 fixed at their lower ends to the lower ejector plate 17 are arranged in parallel and extend through the lower mold support plate 19 the heads of the pins 23 are movable into or out of the accommodating portions 21 formed in the lower mold main body 20 while the lead frame 4 carrying semiconductor chips is placed on the lower mold main body 20 for each cavity block pins 24 are implanted in the main body 20 for positioning the lead frame in place in opposed relation to the upper return pin 13 a lower return pin 25 is mounted on the movable lower mold 2 the lower mold support plate 19 is provided with a guide bush 26 which coacts with the guide pin 14 when the mold assembly is clamped or opened as seen in fig1 the lower mold is provided at a suitable portion with a double acting hydraulic cylinder unit 27 for.