Grain orientation is known to yield high thermal conductivity oriented yttrium silicon oxynitride (Y2O3–Si3N4). However, the anisotropic thermal conductivity of oriented Y2O3–Si3N4 in the stacking direction falls below that of nonoriented Y2O3–Si3N4 and Si3N4 at temperatures above 280 K and 630 K, respectively. Hence, it is unclear will grain orientation actually lead to better heat diffusions from the InGaAs/AlAsSb ultrafast all-optical cross-phase modulators or any other semiconductor devices to the oriented Y2O3–Si3N4 thin-film. To probe into this, the heat diffusion in an InGaAs/AlAsSb ultrafast all-optical cross-phase modulator whereby nonoriented and oriented Y2O3–Si3N4 thin-films are used as the heat-spreader is performed. Analysis shows that grain orientation in Y2O3–Si3N4 thin-film reduces the thermal resistance at the device-film interface through reduced void density, and leads to a marginally better heat diffusion in the device compared to nonoriented Y2O3–Si3N4 thin-film. Consequently- - , oriented Y2O3–Si3N4 thin-film heat-spreader improves the power-handling of the InGaAs/AlAsSb ultrafast all-optical cross-phase modulator by ∼0.46–∼1.8 times of the original value compared to ∼0.36–∼1.75 times of the original value for the case of nonoriented Y2O3–Si3N4 thin-film heat-spreader.