Conformational studies of triethylchlorosilane (TECS) and triethylbromosilane (TEBS) and the elucidation of their gas phase molecular structures have been accomplished by the combined use of theoretical (ab initio and density functional theory) calculations and experimental data from gas phase electron diffraction experiments. Additionally, analysis of the experimental features observed in the IR and Raman spectra recorded for both compounds has allowed us to propose a complete description of the vibrational spectra of both compounds, including an explanation of certain bands, which can only be correctly assigned when more than one conformer is considered to be present.