Insulating thermally conductive sheet

An insulating thermally conductive sheet of a cured product of a thermally conductive silicone resin composition comprising:

• (A) 100 parts by mass of a thermosetting silicone resin containing the following components (A1) to (A3) of
• (A1) an organopolysiloxane having two or more silicon atom-bonded alkenyl groups in each molecule,
• (A2) an organohydrogenpolysiloxane in an amount such that a molar ratio of the total amount of hydrosilyl groups in the component (A2) to the amount of the silicon atom-bonded alkenyl groups in the component (A1) is 0.7 to 1.2, said organohydrogenpolysiloxane being composed of the following components (A2-a) and (A2-b) of
• (A2-a) an organohydrogenpolysiloxane defined by the following formula (a):
• wherein m is 2 or 3, n is a number of 10 to 50, and the bonding arrangement of siloxane units each identified by m and n in brackets may be blocked or random, and
• (A2-b) an organohydrogenpolysiloxane defined by the following formula (b):
• wherein p is a number of 10 to 30,
• wherein a molar ratio between the components (A2-a) and (A2-b) is determined such that the component (A2-a):the component (A2-b)=1:0.2 to 1:2, and
• (A3) a hydrosilylation catalyst in an amount of 100 to 3,000 ppm in terms of platinum group metal atom per 100 parts by mass of the component (A1);
• and
• (B) 150 to 500 parts by mass of a boron nitride that has an average particle diameter of 40 to 100 μm as determined by a laser diffraction/scattering method and an aspect ratio of 20 to 100,
• wherein the insulating thermally conductive sheet has an orientation degree as determined by an X-ray diffraction method in a thickness direction such that (Sum of the counts at [2θ=41 to 43°])/(Sum of the counts at [2θ=25 to 27°]) is 1 or greater.