To provide a die bond agent providing a cured material having excellent adhesive strength and workability, and heat resistance, light resistance and crack resistance; and to provide an optical semiconductor device in which an optical semiconductor element is die bonded with the same.

The die bond agent contains 100 parts by mass of (A)(A-1) an organopolysiloxane having (3,5-diglycidylisocyanuryl)alkyl groups at least on both terminals of the main chain, an amount of (B) a curing agent, the amount being such that the equivalent of the reactive group in the (B) component is 0.4 to 1.5 with respect to 1 equivalent of an epoxy group in the (A) component, 350 to 800 parts by mass of (C) a conductive powder having a particle diameter of ≤20 μm at a cumulative frequency of 90% as measured by laser diffractometry, and having a specific surface area of 0.2 to 1.5 m²/g with respect to 100 parts by mass of the total of the (A) component and the (B) component, and 0.05 to 3 parts by mass of (D) a curing catalyst with respect to 100 parts by mass of the total of the (A) component and the (B) component.