A high-temperature mass-spectrometric study of the vaporization of (silicon + boron nitride) from a boron-nitride Knudsen cell was conducted in the temperature range T = 1688 K to 1921 K. The partial pressures of Si(g), Si-2(g), N-2(g), and Si2N(g) were determined. The dissociation reaction : Si2N(g)= 2Si(g) + 0.5N(2)(g) was evaluated by using new thermal functions for Si2N(g) calculated from the results of recent theoretical and experimental studies, and Delta(r)H(m) degrees values : (538.0 +/- 12.4) kJ . mol(-1) at T -->0, and (545.1 +/- 12.4) kJ . mol(-1) at T = 298.15 K were deduced by third-law evaluation. These values, in combination with the molar dissociation enthalpy of N-2(g) yielded the molar atomization enthalpies : Delta(st)H(m) degrees(Si2N,g) = (1008.8 +/- 12.4) kJ . mol(-1) at T --> 0, and (1017.8 +/- 12.4) kJ . mol(-1) at T = 298.15 K, and in combination with the standard molar enthalpy of formation of Si(g) yielded : Delta(f)H(m) degrees(SI2N, g) = (354.0 +/- 14.8) kJ . mol(-1) at T --> 0, and (355.6 +/- 14.8) kJ . mol(-1) at T = 298.15 K.