Insulated circuit board

An insulated circuit board comprising:

• a ceramic substrate;
• a circuit layer that is bonded to one surface of the ceramic substrate and on which a circuit pattern is to be formed;
• and
• a metal layer bonded to the other surface of the ceramic substrate,
• wherein the circuit layer has a first circuit layer that is bonded to the ceramic substrate and is made of aluminum or an aluminum alloy, and a second circuit layer that is bonded to an upper surface of the first circuit layer and is made of copper or a copper alloy,
• the metal layer has a first metal layer that is bonded to the ceramic substrate and is made of aluminum or an aluminum alloy, and a second metal layer that is bonded to an upper surface of the first metal layer and is made of copper or a copper alloy,
• thicknesses of the first circuit layer and the first metal layer are equal to each other and are 0.2 mm or more and 0.9 mm or less,
• the second circuit layer has a thickness T1 of 0.65 mm or more and 2.0 mm or less,
• an area ratio S1/S2 of a bonding area S1 of the circuit layer to the ceramic substrate to a bonding area S2 of the metal layer to the ceramic substrate is 0.5 or more and 0.8 or less, and a thickness ratio T1/T2 of the thickness T1 of the second circuit layer to a thickness T2 of the second metal layer is 1.4 or more and 3.2 or less.