A thermosetting resin compositing having an essential component (A) organopolysiloxane containing a compound represented by following general formula (1) or (2) and optical semiconductor peripheral material using the composition. [Herein, in the formulas, R1 independently represents a substituted or non-substituted monovalent hydrocarbon radical with the carbon number of 1 to 10, R2 represents an epoxy group-containing organic group, R3 represents R1 or R2, a independently represents an integer of 2 or more, b independently represents an integer of 0 or more, X represents general formula (3), Y represents -o- or a bivalent hydrocarbon radical with the carbon number of 1 to 6, Z represents following formula (4), R1 in the formula independently represents a substituted or non-substituted monovalent hydrocarbon radical with the carbon number of 1 to 10, and c represents an integer of 0 or more.]