Resin for optical-semiconductor-element encapsulation and optical semiconductor device obtained with the same

The present invention relates to a resin for optical-semiconductor-element encapsulation obtained by reacting a silicon compound with a boron compound or an aluminum compound, wherein the silicon compound is represented by the following formula (I): wherein R1 and R2 each independently represent an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, or an aryl group, in which a plurality of R1's are the same or different and a plurality of R2's are the same or different; X represents a hydroxy group, an alkoxy group, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, or an aryl group; and n is 4 to 250, and an optical semiconductor device obtained with the resin.