To provide a photosemiconductor-sealing resin having a higher refractive index than that of a silicone resin while maintaining a heat resistance substantially equivalent to that of the silicone resin, and also a photosemiconductor device obtained by sealing the photosemiconductor element by using the resin, having an improved optical unloading efficiency.

This photosemiconductor-sealing resin containing a polyborosiloxane obtained by reacting a silicon compound with a boron compound is characterized in that the silicon compound is expressed by formula (I) (wherein, R1, R2are each independently an alkyl or phenyl group; and X1, X2are each independently an alkoxy, or hydroxy group or a halogen), and in all of the R1and R2of the silicon compound to be used, the phenyl group occupies ≥50 mol%. The photosemiconductor device is provided by sealing the photosemiconductor element by using the sealing resin for the photosemiconductor.

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