A heat dissipation component for a semiconductor element, the heat dissipation component comprising: a sheet-shaped aluminum-diamond composite containing 50-80 vol% of a diamond powder in which a first peak in a volumetric distribution of particle sizes occurs at 5-25 μm and a second peak occurs at 55-195 μm, and a ratio between an area of a volumetric distribution of particle sizes of 1-35 μm and an area of a volumetric distribution of particle sizes of 45-205 μm is from 1:9 to 4:6, wherein particle size is measured by adding the diamond powders to pure water to produce a slurry as the measurement solution, then measuring the measurement solution with a spectrophotometer using a refractive index of 1.33 for water and a refractive index of 2.42 for diamond, and computing the ratio of the areas in the volumetric distribution by means of the ratio of the cumulative distribution at prescribed particle sizes, the composite comprising an aluminum-containing metal as the balance; wherein the composite is covered, on both main surfaces, with a surface layer, having an average thickness of 0.03-0.2 mm, containing 80 vol% or more of an aluminum-containing metal, two or more Ni-containing layers are formed on at least the surface layer, the Ni-containing layers being such that a first layer from the surface layer side is an amorphous Ni alloy layer having an average thickness of 0.1-2.0 μm and a second layer is an amorphous Ni alloy layer having an average thickness of 0.5-10.0 μm, furthermore, an Au layer having an average thickness of 0.01-4 μm is formed as an outermost layer, and the amorphous Ni alloy layer forming the first layer has a peel strength of 50 N/cm or higher, wherein peel strength is measured as indicated in the description, and average thickness is measured by using an industrial microscope to observe a cross-section of the aluminum-diamond composite, and measuring the thickness of the surface layer on each of the surfaces at five equidistantly spaced locations including the center point and both ends, then computing the average value thereof, wherein the aluminum-containing metal is selected from the group, consisting of aluminum alloy and pure aluminum. a sheet-shaped aluminum-diamond composite containing 50-80 vol% of a diamond powder in which a first peak in a volumetric distribution of particle sizes occurs at 5-25 μm and a second peak occurs at 55-195 μm, and a ratio between an area of a volumetric distribution of particle sizes of 1-35 μm and an area of a volumetric distribution of particle sizes of 45-205 μm is from 1:9 to 4:6, wherein particle size is measured by adding the diamond powders to pure water to produce a slurry as the measurement solution, then measuring the measurement solution with a spectrophotometer using a refractive index of 1.33 for water and a refractive index of 2.42 for diamond, and computing the ratio of the areas in the volumetric distribution by means of the ratio of the cumulative distribution at prescribed particle sizes, the composite comprising an aluminum-containing metal as the balance; wherein the composite is covered, on both main surfaces, with a surface layer, having an average thickness of 0.03-0.2 mm, containing 80 vol% or more of an aluminum-containing metal, two or more Ni-containing layers are formed on at least the surface layer, the Ni-containing layers being such that a first layer from the surface layer side is an amorphous Ni alloy layer having an average thickness of 0.1-2.0 μm and a second layer is an amorphous Ni alloy layer having an average thickness of 0.5-10.0 μm, furthermore, an Au layer having an average thickness of 0.01-4 μm is formed as an outermost layer, and the amorphous Ni alloy layer forming the first layer has a peel strength of 50 N/cm or higher, wherein peel strength is measured as indicated in the description, and average thickness is measured by using an industrial microscope to observe a cross-section of the aluminum-diamond composite, and measuring the thickness of the surface layer on each of the surfaces at five equidistantly spaced locations including the center point and both ends, then computing the average value thereof, wherein the aluminum-containing metal is selected from the group, consisting of aluminum alloy and pure aluminum.