A composition for ceramic substrates that includes a mixture of borosilicate glass powder and ceramic powder. The borosilicate glass powder contains 4% to 8% by weight B2O3, 38% to 44% by weight SiO2, 3% to 10% by weight Al2O3, and 40% to 48% by weight MO, where MO is at least one selected from CaO, MgO, and BaO. The mixing proportions of the borosilicate glass powder and the ceramic powder are 50% to 56% by weight the borosilicate glass powder and 50% to 44% by weight the ceramic powder. The ceramic powder has an average particle diameter D50 of 0.4 to 1.5 μm.