Silicon-substituted hydroxyapatite (SiHA) bioceramics are widely used as bone replacement materials. There are various synthesis methods used to produce SiHA samples using different sources of silicon. This study aims to investigate the role of tetraethyl orthosilicate (TEOS) as the silicon source in the precipitation reaction synthesis of silicate-substituted HA. Four different synthesis methods were studied by changing the order of addition of the TEOS solution during the precipitation reaction. XRD and QXRD were used to determine the phase purity of the prepared samples. FTIR and SSNMR were used to assess silicon/silicate substitution in the prepared materials. Of the initial four methods used, only one resulted in a sample that was phase pure. The other three syntheses, which produced biphasic compositions, were modified and a further single phase sample was prepared. Results showed that the final composition is strongly dependant on how and when the TEOS was added during the precipitation reaction.