PURPOSE: To surely protect wire formed on a substrate surface from the flow of cooling medium, and simplify mounting, by forming an upper cover by inserting strip type sheets between grooves of each package so as to perpendicularly intersect which gooves are adjacent and face each other.

CONSTITUTION: An LSi 12 contains semiconductor elements, and a heat dissipating plate wherein cooling fins 3 are fixed on the upper surface is arranged. Shallow grooves 12-1a of fine width are formed in an endless type on the four side surfaces of a package 12-1 wherein many lead terminals 12-2 are arranged on the lower surface. Strip type sheets 14-1, 14-2 composed of a synthetic resin thin plate are inserted, in X and Y directions, into the grooves 12-1a formed on each surface of the package 12-1 of the LSi 12, thereby forming an upper cover 14. L-shaped side surface covers 15, 16 composed of synthetic resin are fixed on the grooves 12-1a formed on the side surfaces of the package 12-1.