Abstract: When a large-sized silicon nitride substrate having high thermal conductivity is produced, a portion where the thermal conductivity is low is generated, which causes reduction in yield (pass rate). Provided is a silicon nitride substrate in which ?e/?c, which is a ratio of a thermal conductivity ?c at a center portion of the substrate to a thermal conductivity ?e at an end portion of the substrate, is 0.85 to 1.15. Preferably, the silicon nitride substrate has a size of 150 mm×150 mm or more. In the silicon nitride substrate, the ?c and the ?e each are preferably 100 W/m·K or more.

Abstract: Color unevenness generated on a surface of a silicon nitride substrate is reduced. A silicon nitride substrate formed by nitriding silicon containing in a sheet-shaped green body includes a first surface and a second surface opposite to the first surface. In this case, when color difference between a center and an edge of at least one surface of the first surface and the second surface is expressed to be “?E*ab”, a relation “?E*ab?1.5” is established.

Abstract: A silicon nitride substrate including a first surface, and a second surface disposed opposite the first surface. One of the first surface or the second surface is a measurement surface. On the measurement surface, a value of an average full-width-at-half-maximum (FWHM) Cave is broader than 0 cm?1 and narrower than 5.32 cm?1 as measured by using a following measurement method. The measurement method of the average full-width-at-half-maximum (FWHM) Cave: one central point and four edge portions on the measurement surface are determined as measurement points; a Raman spectrum is measured at each of the measurement points; a full-width-at-half-maximum (FWHM) C of a spectral peak having the maximum strength within a range from 850 cm?1 or greater to 875 cm?1 or less is calculated in each Raman spectrum; and an average value of thus calculated full-width-at-half-maximum (FWHM)s C is the average full-width-at-half-maximum (FWHM) Cave.