Abstract: A resin for sealing a compound semiconductor is here disclosed which contains, as a matrix, a siloxane compound for producing a silicone resin by addition reaction and which has a group comprising the bond of an organic group and an oxy group. The group comprising the bond of the organic group and the oxy group bonds to a terminal of the molecule of the siloxane compound, and as this group comprising the bond, 0.1 to 10% by weight, preferably 0.1 to 1.5% by weight of an alkoxy group (--OR') is used. A compound semiconductor chip is covered with the resin for sealing the compound semiconductor and then reacted under predetermined conditions to produce a silicone resin and simultaneously to chemically bond a siloxane group (--Si--O--) in the silicone resin to an element in a portion of the compound semiconductor chip which comes in contact with the silicone resin.