A cost-effective route to synthesize β-SiAlONs from Si mixture by reaction bonding followed by post-sintering was investigated. Three different z values, 0.45, 0.92 and 1.87 in Si6-zAlzOzN8-z, without excess liquid phase were selected to elucidate the mechanism of both SiAlON formation and densification. For the RBSN(reaction-bonded silicon nitride) specimens, nitridation rate of more than 90% was achieved by multistep heating up to 1400oC in flowing 5%H2-95%N2 and residual Si was not detected by XRD analysis. Increase in density was observed with z values for the post-sintered specimens and this tendency was well explained by the presence of higher amount of transient liquid phase with larger z values. Measured z values of the synthesized -SiAlONs were nearly similar to calculated values using starting compositions. The slight deviation in the two z values was successfully explained by the reasonable assessment of nitriding and post-sintering process.